Overview

XOMA Ltd. (“XOMA”), a Bermuda company, is a leading biopharmaceutical company in the field of therapeutic antibody discovery and development. XOMA’s pipeline includes both proprietary products and collaborative programs at various stages of preclinical and clinical development primarily directed toward treatments for cancer and immune disorders. XOMA possesses a broad technology platform for the discovery, optimization and manufacture of therapeutic antibodies as well as a fully integrated product development infrastructure for antibodies and other biologics. We receive royalties from Genentech, Inc. (“Genentech”) on two approved products, RAPTIVA ^® , which is marketed in the United States, Europe and elsewhere, for the treatment of moderate-to-severe plaque psoriasis, and LUCENTIS ^® , a new drug for the treatment of neovascular (wet) age-related macular degeneration, which is marketed in the United States and Europe. We also have future royalty interests in additional therapeutic antibody product candidates being developed by others as a result of licensing our technologies. In addition to supporting our product pipeline, we use our infrastructure to provide process development and manufacturing services on a fee-for-service basis.

Strategy

Our strategy is to develop, manufacture and gain licensure for antibodies and other recombinant protein products to treat cancer, immunological and inflammatory disorders, and infectious diseases. In addition to our own proprietary products, we broaden our pipeline by leveraging our development and manufacturing infrastructure through collaborations with other companies and research institutions. Our goal is to reduce our cash burn and drive towards profitability while continuing to strengthen our product pipeline. We recognize the challenging nature of this goal, and the principal elements of our strategy are to:

1

Table of Contents

Products

Below is a summary of our current products and stages of clinical development:

XOMA has a financial interest in two marketed antibody products and a third that has been submitted for regulatory approval, and is developing other antibody and protein therapeutic products. These products are listed below in order of their development status, beginning with the most advanced:

In 2006, Serono announced the results of the 24-week Clinical Experience Acquired with RAPTIVA ^® (“CLEAR”) study to evaluate RAPTIVA ^® in moderate-to-severe psoriasis patients and refractory patients. The CLEAR study confirmed the efficacy and safety of RAPTIVA ^® during the initial 12-week treatment period and demonstrated a continued improvement in clinical response for patients following an extended treatment. RAPTIVA ^® was also found to be equally effective in the subgroup of patients refractory to at least two systemic therapies. In 2006, Serono also initiated CLEAREST ^™ in Europe with a seven year trial, the first large-scale pharmaco-epidemiological study of RAPTIVA ^® in psoriasis in Europe. The primary objective of this prospective, seven year cohort study is to gather additional long-term safety data of RAPTIVA ^® in 7,000 adult patients with moderate-to-severe plaque psoriasis over approximately 18,000 patient years of clinical treatment. In February of 2007, Genentech announced results from a 12-week Phase IV study of RAPTIVA ^® that showed statistically significant improvement in patients with chronic moderate-to-severe plaque psoriasis involving the hands and feet. The study was the first randomized, double blind, placebo-controlled trial to evaluate a biologic agent in the treatment of this uniquely challenged subpopulation of psoriasis patients.

In January of 2007, in conjunction with Harvard Medical School, we initiated an open label, dose escalating Phase I/II clinical trial of NEUPREX ^® in adults and children undergoing allogeneic hematopoietic stem cell transplantation (“HSCT”) to evaluate safety, pharmacokinetics and markers of biological activity. Earlier research indicates that endotoxemia can induce or worsen acute graft vs. host disease in these patients who are also susceptible to infectious complications due to the large doses of radiation or chemotherapy they receive prior to transplantation. We expect to add other sites to this

2

Table of Contents

study during 2007. Success in HSCT trials may be relevant to potential use in acute radiation syndrome as part of the United States Government’s bio-defense efforts.

XOMA is also supporting investigator-initiated trials at University of Texas Southwestern in Dallas in pediatric patients with congenital heart abnormalities requiring open heart surgery at Children’s Hospital and in patients with burn injuries at Parkland Burn Center. These Phase I trials are evaluating opebacan’s safety and its role in improving endotoxin-induced complications in these patient populations. We expect these trials to conclude in 2007 and then evaluate options for conducting additional studies.

In September of 2006, the European Medicines Agency (“EMEA”) granted an orphan medicinal product designation to NEUPREX ^® in meningococcal sepsis, a potentially life-threatening bacterial infection predominantly affecting young children. Meningococcal sepsis is a blood infection caused by the gram-negative bacterium Neisseria meningitidis . We are completing the regulatory assessment for NEUPREX ^® under the EMEA exceptional circumstances mechanism during the first half of 2007 and intend to base our planned application on existing Phase III clinical trial data.

3

Table of Contents

In October of 2004, we entered into an agreement with Triton BioSystems, Inc. (“Triton”) under which Triton has in-licensed the exclusive worldwide right to use the ING-1 monoclonal antibody with Triton’s Targeted Nano-Therapeutics ^™ (“TNT ^™ ”) System. The TNT ^™ System is an innovative product that ablates tumors by using tiny magnetic spheres delivered, to the tumor, systemically with antibodies and heated by means of a magnetic field directed to the tumor. The combination of the ING-1 antibody with the TNT ^™ System is intended to create a novel, highly selective, safe, and effective treatment for adenocarcinomas, such as breast, colorectal, lung, ovary and prostate. ING-1 remains available for licensing outside the field covered by the Triton license.

4

Table of Contents

The following table describes important information related to certain products on which we earn royalties, that we are currently developing or that are available for licensing:

Below is a summary of certain proprietary technologies owned by us and available for licensing to other companies:

5

Table of Contents

We have granted over 45 licenses to biotechnology and pharmaceutical companies to use our patented and proprietary technologies relating to bacterial expression of recombinant pharmaceutical products. Bacterial antibody expression is an enabling technology for the discovery and selection, as well as the development and manufacture, of recombinant protein pharmaceuticals, including diagnostic and therapeutic antibodies for commercial purposes. Bacterial antibody expression is also a key technology used in multiple systems for high-throughput screening of antibody domains. Expression of antibodies by phage display technology, for example, depends upon the expression and secretion of antibody domains from bacteria as properly folded, functional proteins.

Current licensees include but are not limited to the following companies:

These licenses are sometimes associated with broader agreements. For example, in October of 2006, we entered into a licensing and product development agreement with Affimed Therapeutics AG (“Affimed”). Under the terms of the agreement, Affimed received a license to use our BCE technology for research related to recombinant antibody products, with an option to acquire a BCE license for production and commercialization of antibodies, in particular their proprietary TandAb and Flexibody products. In addition, we will provide Affimed with cell line development and process development services specific to a TandAb therapeutic product candidate that they are currently developing. We received a license under Affimed’s antibody library patents for antibody discovery purposes, as well as for the development and commercialization of antibodies. In addition, Affimed will build two customized patient-derived human antibody phage display libraries according to our specifications.

As of February 2, 2007, we were aware of one antibody product, UCB S.A.’s (“UCB”) CIMZIA ^™ , in late-stage clinical testing which is manufactured under a license using our BCE technologies. CIMZIA ^™ (certolizumab pegol, CDP870) is a anti-TNF (Tumor Necrosis Factor) alpha antibody fragment and has been submitted for regulatory approval for Crohn’s disease. It has had positive results in two Phase III trials in rheumatoid arthritis and in one mid-stage clinical trial in psoriasis.

6

Table of Contents

HE ^™ technology was used in our XOMA 052 and certain other antibody products. In 2006, we entered into our first HE ^™ technology service agreements and humanized antibodies for AVEO Pharmaceuticals, Inc. (“AVEO”) and Attenuon, LLC (“Attenuon”).

In addition, we have installed commercially available phage display libraries for the discovery of antibodies and are utilizing XOMA proprietary libraries to enhance our antibody technology platform. We believe that access to multiple libraries offers a number of benefits to XOMA and its partners, by permitting screening of libraries in parallel where feasible to increase our probability of technical and business success in finding those rare and unique, high-affinity antibodies directed to targets of interest. We also have access to certain intellectual property rights and services that augment our existing antibody technology platform and development capabilities and further streamline product development timelines. This broad antibody technology platform and expertise is available for building our antibody product pipeline as well as those of our collaborators.

Our fully integrated infrastructure also allows us to offer technical development and manufacturing services on a fee-for-service basis. In particular, in March of 2005, we were awarded an 18-month contract worth approximately $15.0 million from the National Institute of Allergy and Infectious Diseases (“NIAID”) to develop three anti-botulinum neurotoxin monoclonal antibodies and, in July of 2006, NIAID awarded an additional three year contract worth approximately $16.3 million to produce these antibodies to protect United States citizens against the harmful effects of botulinum neurotoxins used in bioterrism. In November 2006, we were named as a subcontractor under a prime contract between SRI International and NIAID. Once the final terms are negotiated, we will manufacture a variety of monoclonal antibody therapeutic agents of importance to NIAID. We expect the final contract to run five years and total $28.1 million. Successful negotiation of the subcontract would, if the full amount is funded, bring the total of our governmental contract awards to approximately $60.0 million since March of 2005. We are continuing to seek other opportunities for government and biodefense contracts.

Financial and Legal Arrangements of Product Collaborations, Licensing an Other Arrangements

Current Agreements

Genentech

In April of 1996, we entered into a collaboration agreement with Genentech for the development of RAPTIVA ^® . In March of 2003, we entered into amended and expanded agreements related to all aspects of the collaboration, to reflect the then current understanding between the companies. The agreements called for us to share in the development costs and to receive a 25% share of future United States operating profits and losses and a royalty on sales outside the United States. The agreements also called for Genentech to finance our share of development costs up until first FDA marketing approval via a convertible subordinated loan, and our share of pre-launch marketing and sales costs via an additional commercial loan facility. Under the loan agreement, upon FDA approval of the product, which occurred on October 27, 2003, we elected to pay $29.6 million of the development loan in convertible preference shares and to defer repayment of the remaining $40.0 million as an offset against future proceeds from our 25% share of United States operating profits on the product. On December 22, 2003, we issued the preference shares to Genentech which are convertible into approximately 3.8 million common shares at a price of $7.75 per common share. The $13.4 million of outstanding principal and interest on the commercial loan was payable only in cash and was paid in January and May of 2004.

In January of 2005, we announced a restructuring of our arrangement with Genentech on RAPTIVA ^® . Under the restructured arrangement, effective January 1, 2005, we are entitled to receive mid-single digit

7

Table of Contents

royalties on worldwide sales of RAPTIVA ^® in all indications. The previous cost and profit sharing arrangement for RAPTIVA ^® in the United States was discontinued, and Genentech will be responsible for all operating and development costs associated with the product. Genentech may elect and we may agree to provide further clinical trial or other development services at Genentech’s expense. In addition, our obligation to pay the outstanding balance to Genentech of $40.9 million under the development loan, including accrued interest, was extinguished.

In December of 1998, we licensed our BCE technology to Genentech, which utilized it in the development of LUCENTIS ^® for the treatment of neovascular (wet) age-related macular degeneration. LUCENTIS ^® was approved by the FDA in June of 2006 and in the European Union in January of 2007. We are entitled to receive an undisclosed royalty on worldwide sales of LUCENTIS ^® .

Novartis

In February of 2004, we entered into an exclusive, worldwide, multi-product collaboration with Novartis to develop and commercialize antibody products for the treatment of cancer. Under the terms of the agreement, the companies agreed to jointly research, develop, and commercialize multiple antibody product candidates. The companies share expenses and revenues, generally on a 70-30 basis, with our share being 30%. Novartis’ profit share is subject to a limited upward adjustment, which, in turn, may be reduced if we achieve certain milestones. Financial terms include initial payments to us in 2004 totaling $10.0 million and a loan facility, secured by our interest in the collaboration, of up to $50.0 million to fund up to 75% of our share of expenses beginning in 2005. In the first quarter of 2007, Novartis’ and our mutual obligations to conduct antibody discovery, development and commercialization work together on an exclusive basis in oncology expired, except with respect to existing collaboration projects which have reached the development stage.

Lexicon

In June of 2005, we entered into a collaboration agreement with Lexicon to jointly develop and commercialize antibody drugs for certain targets discovered by Lexicon. The collaboration is designed to combine Lexicon’s target discovery and biotherapeutics capabilities with our antibody generation, process development and manufacturing expertise to accelerate the development and commercialization of novel therapeutic antibodies.

During the three-year initial term, Lexicon will select for submission to the collaboration targets from among those discovered and analyzed in its Genome5000 ^™ program. In this program, Lexicon is using its gene knockout technology to discover the physiological functions of 5,000 potential drug targets. Our role is to generate or engineer antibodies that modulate the collaboration’s targets using phage display libraries and our proprietary HE ^™ technology. The companies are sharing the responsibility and costs for research, preclinical, clinical and commercialization activities. Costs and profits are allocated 65% to Lexicon and 35% to us. We will have principal responsibility for manufacturing antibodies for use in clinical trials and commercial sales.

Schering Plough

In May of 2006, we entered into a collaboration agreement with the SPRI division of Schering-Plough Corporation for therapeutic monoclonal antibody discovery and development. Under the agreement, SPRI will make upfront, annual maintenance and milestone payments to us, fund our R&D and manufacturing activities related to the agreement and pay royalties on sales of products resulting from the collaboration. During the collaboration, we will discover therapeutic antibodies against three targets selected by SPRI using multiple human antibody phage display libraries, may optimize antibodies through affinity maturation or other protein engineering, may use our proprietary HE ^™ technology to humanize antibody candidates generated by hybridoma techniques, perform pre-clinical studies to support regulatory filings, develop cell lines and production processes and produce antibodies for initial clinical trials. SPRI selected the first target at the inception of the agreement and, in December of 2006, exercised its right to initiate the additional discovery and development programs.

8

Table of Contents

Takeda

In November of 2006, we entered into a collaboration agreement with Takeda for therapeutic monoclonal antibody discovery and development. During the collaboration, we will discover and optimize therapeutic antibodies against multiple targets selected by Takeda. Under the agreement, Takeda will make upfront, annual maintenance and milestone payments to us, fund our R&D and manufacturing activities for preclinical and early clinical studies and pay royalties on sales of products resulting from the collaboration. Takeda will be responsible for clinical trials and commercialization of drugs after an IND submission and is granted the right to manufacture once the product enters into Phase II clinical trials.

NIAID

In March of 2005, we were awarded a $15.0 million contract from NIAID, a division of the National Institutes of Health, to develop three anti-botulinum neurotoxin monoclonal antibody therapeutics. Under this contract, we created production cell lines using our proprietary antibody expression systems, built Master and Manufacturer’s Working Cell Banks, developed production processes and produced initial quantities of the three antibodies. The contract was performed over an eighteen month period and was 100% funded with Federal funds from NIAID under Contract No. HHSN266200500004C. Final acceptance of the project was received in October of 2006.

In July of 2006, we were awarded a $16.3 million contract funded with Federal funds from NIAID under Contract No. HHSN266200600008C/N01-Al-60008 to produce monoclonal antibodies for the treatment of botulism to protect United States citizens against the harmful effects of botulinum neurotoxins used in bioterrorism. Under this contract, we will create and produce an innovative injectable product comprised of three anti-type A botulinum neurotoxin monoclonal antibodies to support entry into Phase I safety human clinical trials. The work is being performed on a cost plus fixed fee basis, per the terms of the contract, over a three year period.

Taligen

In September of 2006, we entered into an agreement with Taligen Therapeutics, Inc. (“Taligen”) which formalized an earlier letter agreement, which was signed in May of 2006, for the development and Good Manufacturing Practices (“cGMP”) manufacture of a novel antibody fragment for the potential treatment of inflammatory diseases. Under the agreement, we will utilize our BCE technology and expertise to develop and scale-up production processes for Taligen’s FAb antibody fragment and manufacture quantities of the antibody fragment sufficient to support preclinical and initial clinical trials. Taligen will pay all manufacturing costs and, if it elects to exercise its option to obtain a production license for our BCE technology, will make upfront, milestone and royalty payments.

AVEO

In April of 2006, we entered into an agreement with AVEO to utilize our HE ^™ technology to humanize AV-299 under which AVEO paid us an up-front license fee and development milestones. Under this agreement we created four HE ^™ versions of the original AV-299, all of which met design goals and from which AVEO selected one as its lead development candidate. In the future, AVEO will pay annual maintenance fees, additional development milestones and royalties.

In September of 2006, as a result of the successful humanization of AV-299, we entered into a second agreement with AVEO to manufacture and supply AV-299, AVEO’s novel anti-HGF antibody, in support of early clinical trials. Under the agreement, we will create AV-299 production cell lines and conduct process and assay development as well as cGMP manufacturing activities in support of AVEO’s IND filing and early clinical trials. AVEO retains all development and commercialization rights to AV-299.

9

Table of Contents

Attenuon

In September of 2006, we entered into an agreement with Attenuon to utilize our HE ^™ technology to humanize a monoclonal antibody targeting the urokinase plasminogen activator system for the treatment of cancer. Attenuon will pay us an up-front fee, annual maintenance fees, development milestones and royalties. Attenuon will retain all development and commercialization rights to the antibody.

Triton

In October of 2004, we entered into an agreement with Triton under which Triton licensed the exclusive worldwide rights from us to use our ING-1 monoclonal antibody with Triton’s TNT ^™ System. The TNT ^™ System is an innovative product that ablates tumors by using tiny magnetic spheres delivered, to the tumor, systemically with antibodies and heated by means of a magnetic field directed to the tumor. The combination of the ING-1 antibody with the TNT ^™ System is intended to create a novel, highly selective, safe, and effective treatment for adenocarcinomas, such as breast, colorectal, lung, ovary and prostate. The license to Triton includes United States and foreign patent rights related to our ING-1 and HE ^™ technologies along with several pending applications. ING-1 remains available for licensing outside the field covered by the Triton license. Under the terms of the contract, we received an upfront license fee and will receive milestones and royalties.

Millennium

In November of 2001, in conjunction with Millennium, we announced an agreement under which we would collaborate to develop two of Millennium’s biotherapeutic agents, MLN2222 (also known as CAB2) and MLN2201, for certain vascular inflammation indications.

In October of 2003, we announced the discontinuation of development of MLN2201, based on preliminary data from a Phase I study that did not meet predefined criteria necessary to support further product development efforts.

In December of 2003, we announced the initiation of a Phase I clinical program for MLN2222, a complement inhibitor for coronary artery bypass graft surgery targeting vascular inflammation associated with such surgery, to evaluate its safety, tolerability, pharmacokinetic and pharmacodynamic properties. In October of 2004, we announced the amendment of our agreements with Millennium whereby Millennium assumed responsibility for all development work and expenses for MLN2222 upon initiation of Phase II testing. We completed a Phase I trial of MLN2222 and have transferred the relevant clinical data from the trial to Millennium. We are obligated to continue to provide quantities of bulk drug substance and services requested and paid for by Millennium for future clinical trials. We will be entitled to receive an undisclosed royalty on future net sales of MLN2222, as well as payments related to the achievement of certain clinical and regulatory milestones.

Recently Terminated Agreements

Cubist

In September of 2005, we announced that we had signed a letter agreement with Cubist Pharmaceuticals, Inc. (“Cubist”) to develop production processes and to manufacture HepeX-B ^™ , a novel two-antibody biologic, in quantities sufficient to conduct Phase III clinical trials. HepeX-B ^™ is a combination of two fully human monoclonal antibodies that target hepatitis B virus (“HBV”) surface antigens. In July of 2006, Cubist announced that it had decided to cease investment in this product because of stringent FDA requirements for regulatory approval and, as a result, we have terminated our letter agreement with Cubist.

Aphton

In September of 2004, we announced a worldwide collaboration with Aphton Corporation (“Aphton”) to develop treatments for gastrointestinal and other gastrin-sensitive cancers using anti-gastrin monoclonal

10

Table of Contents

antibodies. Under the terms of the agreement, the companies agreed to share all development expenses and all commercialization profits and losses for all product candidates on a 70/30 basis, with our share being 30%. In January of 2006, Aphton announced that its common stock had been delisted from Nasdaq. In May of 2006, Aphton filed for bankruptcy protection under Chapter 11, Title 11 of the United States bankruptcy code and we terminated the agreement. In July of 2006, Receptor BioLogix, Inc. acquired the assets of Aphton.

Other Products

We are seeking development and marketing partners for additional products in our pipeline. No assurance can be given regarding the timing or likelihood of future collaborative arrangements or of product licensure.

We are also pursuing additional opportunities to further broaden our product pipeline. These include product development collaborations with other pharmaceutical and biotechnology companies and evaluations of product in-licensing and acquisition opportunities.

Competition

The biotechnology and pharmaceutical industries are subject to continuous and substantial technological change. Competition in the areas of recombinant DNA-based and antibody-based technologies is intense and expected to increase as new technologies emerge and established biotechnology firms and large chemical and pharmaceutical companies continue to advance in the field. A number of these large pharmaceutical and chemical companies have enhanced their capabilities by entering into arrangements with or acquiring biotechnology companies or entering into business combinations with other large pharmaceutical companies. Many of these companies have significantly greater financial resources, larger research and development and marketing staffs and larger production facilities than ours. Moreover, certain of these companies have extensive experience in undertaking preclinical testing and human clinical trials. These factors may enable other companies to develop products and processes competitive with or superior to ours. In addition, a significant amount of research in biotechnology is being carried out in universities and other non-profit research organizations. These entities are becoming increasingly interested in the commercial value of their work and may become more aggressive in seeking patent protection and licensing arrangements. There can be no assurance that developments by others will not render our products or technologies obsolete or uncompetitive.

Without limiting the foregoing, we are aware that:

11

Table of Contents

In addition to LUCENTIS ^® , there are two other FDA-approved therapies to treat macular degeneration: Pfizer, Inc.’s and OSI Pharmaceuticals, Inc.’s Macugen ^® and Novartis’ and QLT Inc.’s Visudyne ^® . It is also possible that LUCENTIS ^® will compete with Genentech’s cancer drug Avastin ^® .

There are several companies developing topical peptide treatments which may compete with XOMA 629 in acne. Migenix Inc. and its partner Cutanea Life Sciences, Inc. are developing CLS001 (formerly MBI 594AN) for roseasea, a topical peptide that has completed two Phase II trials for the treatment of acne. Helix Biomedix, Inc. is developing several peptide compounds. Medicis Pharmaceutical Corp. has rights to human derived antimicrobial peptides that may be developed for acne.

In collaboration with Novartis, we are co-developing a humanized antibody to the target CD40, and, at the current time, there are several CD40-related programs under development, mostly focused on the development of CD40 ligand products. For example, SGN-40 is a humanized monoclonal antibody under development by Seattle Genetics, Inc. (“Seattle Genetics”) which is targeting CD40 antigen. Seattle Genetics is currently conducting a phase II clinical trial for patients with diffuse large B-cell lymphoma, the most common type of aggressive non-Hodgkin’s lymphoma, and phase I trials for patients with multiple myeloma or chronic lymphocytic leukemia. In January of 2007, Seattle Genetics entered into an exclusive worldwide license agreement with Genentech to develop and commercialize SGN-40. Under the agreement, Genentech will fund future research, development, manufacturing and commercialization costs. In January of 2007, Kirin Brewery Company, Limited and Astellas Pharma Inc. announced that they have entered into a license and collaborative research and development agreement under which they will exclusively collaborate in developing and marketing a fully human anti-CD40 antagonistic monoclonal antibody worldwide with a first target indication of prophylaxis of organ rejection associated with organ transplantation.

It is possible that other companies may be developing other products based on the same human protein as our NEUPREX ^® product, and these products may prove to be more effective than NEUPREX ^® . It is also possible that other companies may be developing other products based on the same therapeutic target as our XOMA 052 product and these products may prove to be more effective than XOMA 052.

Regulatory

Our products are subject to comprehensive preclinical and clinical testing requirements and to approval processes by the FDA and by similar authorities in other countries. Our products are primarily regulated on a

12

Table of Contents

product-by-product basis under the United States Food, Drug and Cosmetic Act and Section 351(a) of the Public Health Service Act. Most of our human therapeutic products are or will be classified as biologic products. Approval of a biologic for commercialization requires licensure of the product and the manufacturing facilities. The review of therapeutic biologic products is carried out by the FDA’s Center for Drug Evaluation and Research, the body that also reviews drug products.

The FDA regulatory process is carried out in several phases. Prior to beginning human clinical testing of a proposed new biologic product, an IND is filed with the FDA. This document contains scientific information on the proposed product, including results of testing of the product in animal and laboratory models. Also included is information on manufacture of the product and studies on toxicity in animals and a clinical protocol outlining the initial investigation in humans.

The initial stage of clinical testing, Phase I, ordinarily encompasses safety, pharmacokinetic and pharmacodynamic evaluations. Phase II testing encompasses investigation in specific disease states designed to provide preliminary efficacy data and additional information on safety. Phase III studies are designed to further establish clinical safety and efficacy and to provide information allowing proper labeling of the product following approval. Phase III studies are most commonly multi-center, randomized, placebo-controlled trials in which rigorous statistical methodology is applied to clinical results. Other designs may also be appropriate in specific circumstances.

Following completion of clinical trials, a Biologics License Application is submitted to the FDA to request marketing approval. Internal FDA committees are formed that evaluate the application, including scientific background information, animal and laboratory efficacy studies, toxicology, manufacturing facility and clinical data. During the review process, a dialogue between the FDA and the applicant is established in which FDA questions are raised and additional information is submitted. During the final stages of the approval process, the FDA generally requests presentation of clinical or other data before an FDA advisory committee, at which point, some or all of such data may become available. Also, during the later stages of review, the FDA conducts an inspection of the manufacturing facility to establish that the product is made in conformity with good manufacturing practice. If all outstanding issues are satisfactorily resolved and labeling established, the FDA issues a license for the product and for the manufacturing facility, thereby authorizing commercial distribution.

The FDA has substantial discretion in both the product approval process and the manufacturing approval process. It is not possible to predict at what point, or whether, the FDA will be satisfied with our submissions or whether the FDA will raise questions which may delay or preclude product approval or manufacturing facility approval. As additional clinical data is accumulated, it will be submitted to the FDA and may have a material impact on the FDA product approval process. Given that regulatory review is an interactive and continuous process, we have adopted a policy of limiting announcements and comments upon the specific details of the ongoing regulatory review of our products, subject to our obligations under the securities laws, until definitive action is taken. There can be no assurance any of the products we have under development will be developed successfully, obtain the requisite regulatory approval or be successfully manufactured or marketed.

In Europe, most of our human therapeutic products are or will be classified as biological medicinal products which are assessed through a centralized procedure by the EMEA. The EMEA coordinates the evaluation and supervision of medicinal products throughout the European Union and the European Economic Area. The assessment of the Marketing Authorization (“MA”) Application is carried out by a Rapporteur and a Co-rapporteur appointed by the Committee for Medicinal Products for Human Use ( “ CHMP ” ), which is the expert scientific committee of the EMEA.

The Rapporteur and Co-rapporteur are drawn from the CHMP membership representing member states of the European Union. In addition to their responsibility for undertaking scientific assessments of an application for a MA, the Rapporteur and the Co-Rapporteur liaise with the applicant on behalf of the CHMP in an effort to provide answers to queries raised by the CHMP. Their assessment report(s) is circulated to and considered by the

13

Table of Contents

full CHMP membership, leading to the production ultimately of a CHMP opinion which is transmitted to the applicant and the European Commission. The final decision on the grant of a MA is made by the Commission as the licensing authority of the European Community (“Community”). Under Community law, a positive decision issued by the European Commission represents the grant of a MA. Such an authorization allows a medicinal product to be placed on the European market. Upon the grant of an MA in the European Union, certain member states require pricing approval before the product can be placed into commercial distribution.

Under Community law, the applicant may request grant of a MA under exceptional circumstances if comprehensive data on the efficacy and safety of the drug, under normal conditions of use cannot be provided because its intended indications are encountered so rarely (such as in the case of a medicinal product intended for treating an orphan disease) that comprehensive evidence cannot reasonably be collected, the present state of scientific knowledge will not allow comprehensive information to be collected, or it would be against generally accepted medical ethics to collect comprehensive information. The Rapporteur, Co-Rapporteur and the other CHMP members will assess the justification/data submitted for exceptional circumstances as part of the overall assessment of the benefit/risk of the application. It is up to the CHMP, during the review, to ultimately decide on whether grant of a MA under exceptional circumstances is justified on the evidence before them. Approval under exceptional circumstances is subject to a requirement for specific procedures related to safety and results of its use and is reviewed annually to reassess the risk-benefit balance of the product. Once approval is granted, the product can be marketed under the single European MA in all member states of the European Union and the European Economic Area. Consistent with the single MA, the labeling for Europe is identical throughout all member states except that all labeling must be translated into the local language of the country of intended importation and in relation to the content of the so called “ blue box ” on the outer packaging in which locally required information may be inserted.

Orphan drugs are those intended for use in rare diseases or conditions. As a result of the high cost of development and the low return on investment for rare diseases, governments provide regulatory and commercial incentives for the development of drugs for small disease populations. In the United States, the term “rare disease or condition” means any disease or condition which affects less than 200,000 persons in the United States. Applications for United States orphan drug status are evaluated and granted by the Office of Orphan Products Development (“OOPD”) of the FDA. In the United States, orphan drugs are subject to the standard regulatory process for marketing approval but are exempt from the payment of user fees for licensure, receive market exclusivity for a period of seven years and some tax benefits, and are eligible for OOPD grants. In Europe, orphan medicinal products are those intended for the diagnosis, prevention or treatment of a life-threatening or chronically debilitating condition affecting not more than five in 10,000 persons in the Community. The EMEA’s Committee for Orphan Medicinal Products (“COMP”) reviews applications seeking orphan designation. If the European Commission agrees with a positive assessment made by COMP, then the product will receive a positive designation through adoption of a decision by the European Commission. Orphan medicinal products are exempt from fees for protocol assistance and scientific advice from the Scientific Advice Working Party during development, reduction or exemption of MA and other fees, and ten year market exclusivity upon granting of a MA in respect of the approved clinical indication. Moreover, manufacturers may be eligible for grants or other financial incentives from the Community and Member States programs.

Patents and Trade Secrets

As a result of our ongoing activities, we hold and are in the process of applying for a number of patents in the United States and internationally to protect our products and important processes. We also have obtained or have the right to obtain exclusive licenses to certain patents and applications filed by others. However, the patent position of biotechnology companies generally is highly uncertain and no consistent policy regarding the breadth of allowed claims has emerged from the actions of the U.S. Patent and Trademark Office (“Patent Office”) with respect to biotechnology patents. Accordingly, no assurance can be given that our patents will afford protection against competitors with similar technologies, or others will not obtain patents claiming aspects similar to those covered by our patent applications.

14

Table of Contents

We have established an extensive portfolio of patents and applications related to our BPI-related products, including novel compositions, their manufacture, formulation, assay and use. We are also the exclusive licensee of BPI-related patents and applications owned by New York University (“NYU”), including those directed to novel BPI-related protein and DNA compositions, as well as their production and uses. Finally, we are the exclusive licensee of BPI-related patents and applications owned by Incyte Corporation (“Incyte”), including those related to endotoxin-associated uses of BPI.

We have established a portfolio of patents related to our bacterial expression technology, including claims to novel promoter sequences, secretion signal sequences, compositions, methods for expression and secretion of recombinant proteins from bacteria, including immunoglobulin gene products, and improved methods and cells for expression of recombinant protein products. U.S. Patent No. 5,028,530 is directed to expression vehicles containing an araB promoter, host cells and processes for regulated expression of recombinant proteins. U.S. Patent Nos. 5,576,195 and 5,846,818 are related to DNA encoding a pectate lyase signal sequence, recombinant vectors, host cells and methods for production and externalization of recombinant proteins. U.S. Patent Nos. 5,595,898, 5,698,435 and 5,618,920 address secretable immunoglobulin chains, DNA encoding the chains and methods for their recombinant production. U.S. Patent Nos. 5,693,493, 5,698,417 and 6,204,023 relate to methods for recombinant production/secretion of functional immunoglobulin molecules. U.S. Patent No. 7,094,579 relates to eukaryotic signal sequences and their use in methods for prokaryotic expression of recombinant proteins. U.S. Patent No. 6,803,210 relates to improved bacterial host cells that are deficient in one or more of the active transport systems for an inducer of an inducible promoter, such as arabinose for an araB promoter, and methods for the use of such cells for the production of recombinant proteins.

We have also established a portfolio of patent applications related to our mammalian expression technology, including U.S. Patent Application Publication No. 2003/0203447 for which we have received a Notice of Allowance, related to methods and materials for increasing the expression of recombinant polypeptides using expression vectors containing multiple copies of a transcription unit encoding a polypeptide of interest.

We have established a portfolio of patents and applications related to our HE ^™ technology, including U.S. Patent No. 5,766,886, directed to methods of modifying antibody variable domains to reduce immunogenicity. Related patents and applications are directed to antibodies engineered according to our patented methods. We believe that our patented HE ^™ technology provides an attractive alternative to other humanization technologies.

If certain patents issued to others are upheld or if certain patent applications filed by others issue and are upheld, we may require certain licenses from others in order to develop and commercialize certain potential products incorporating our technology. There can be no assurance that such licenses, if required, will be available on acceptable terms.

Research and License Agreements

We have contracted with a number of academic and institutional collaborators to conduct research and development activities. Under these agreements, we generally fund either the research and development or evaluation of products, technologies or both, will own or obtain exclusive licenses to products or technologies developed and may pay royalties on sales of products covered by certain licenses. The rates and durations of such royalty payments vary by product and institution and range, generally, for periods from five years to indefinite duration. Aggregate expenses incurred by us under all of our research agreements were negligible for each of 2006, 2005 and 2004. We have entered into certain license agreements with respect to the following products:

15

Table of Contents

Each party has the right to terminate the agreement upon a material breach by the other party of the performance of its obligations under the agreement, subject to customary cure periods. Upon termination of the agreement prior to the expiration of the relevant patents, all rights in and to NYU’s intellectual property revert to NYU.

The agreement expires in July of 2008 unless, on or prior to such date, the license granted therein becomes fully paid up in accordance with its terms. Incyte has the right to terminate the agreement (subject to a customary cure period) upon a breach by us of any of our material obligations under the agreement.

International Operations

We believe that, because the pharmaceutical industry is global in nature, international activities will be a significant part of our future business activities and that, when and if we are able to generate income, a substantial portion of that income will be derived from product sales and other activities outside the United States.

A number of risks are inherent in international operations. Foreign regulatory agencies often establish standards different from those in the United States. An inability to obtain foreign regulatory approvals on a timely basis could have an adverse effect on our international business, financial condition and results of operations. International operations may be limited or disrupted by the imposition of government controls, export license requirements, political or economic instability, trade restrictions, changes in tariffs, restrictions on repatriating profits, taxation or difficulties in staffing and managing international operations. In addition, our business, financial condition and results of operations may be adversely affected by fluctuations in currency exchange rates. There can be no assurance that we will be able to successfully operate in any foreign market.

We were incorporated in Delaware in 1981 and became a Bermuda company effective December 31, 1998, when we completed a shareholder-approved corporate reorganization, changing our legal domicile from Delaware to Bermuda and our name to XOMA Ltd. When referring to a time or period before December 31, 1998, or when the context so requires, the terms “Company” and “XOMA” refer to XOMA Corporation, a Delaware corporation and the predecessor of XOMA Ltd.

Employees

As of December 31, 2006, we employed 255 non-unionized full-time employees at our California facilities, principally in Berkeley, California, and one employee in Ireland. Our employees are engaged in clinical, process development and manufacturing, quality assurance and control, research and product development, and in executive, finance and administrative positions. We consider our employee relations to be excellent.

16

Table of Contents

Available Information

For information on XOMA’s investment prospects and risks, please contact Mr. Paul Goodson, Senior Director, Investor Relations and Corporate Communications at (800) 246-9662 or by sending an e-mail message to investorrelations@xoma.com. Our principal executive offices are located at 2910 Seventh Street, Berkeley, California 94710 U.S.A. Our telephone number is (510) 204-7200.

The following information can be found on our website at http://www.xoma.com or can be obtained free of charge by contacting our Investor Relations Department:

We intend to satisfy the applicable disclosure requirements regarding amendments to, or waivers from, provisions of our Code of Ethics by posting such information on our website.

The following risk factors and other information included in this annual report should be carefully considered. The risks and uncertainties described below are not the only ones we face. Additional risks and uncertainties not presently known to us also may impair our business operations. If any of the following risks occur, our business, financial condition, operating results and cash flows could be materially adversely affected.

Our present and future revenues rely significantly on sales of products marketed and sold by others.

Currently, our revenues rely significantly upon sales of RAPTIVA ^® and LUCENTIS ^® , in which we have only royalty interests. RAPTIVA ^® was approved by the FDA on October 27, 2003, for the treatment of chronic moderate-to-severe plaque psoriasis in adults who are candidates for systemic therapy or phototherapy. Genentech and Serono, Genentech’s international marketing partner for RAPTIVA ^® , are responsible for the marketing and sales effort in support of this product. In September of 2004, Serono announced that RAPTIVA ^® had received approval for use in the European Union and the product was launched in several European Union countries in the fourth quarter of 2004. In January of 2007, Merck KGaA acquired Serono and renamed the surviving entity Merck Serono S.A. We are evaluating the impact of this acquisition but do not yet know what effect it will have on sales of RAPTIVA ^® . LUCENTIS ^® was approved by the FDA on June 30, 2006, for the treatment of age-related macular degeneration. Genentech and Novartis, Genentech’s international marketing partner for LUCENTIS ^® , are responsible for the marketing and sales effort in support of this product. We have no role in marketing and sales efforts, and Genentech, Serono and Novartis do not have an express contractual obligation to us regarding the marketing or sales of RAPTIVA ^® or LUCENTIS ^® .

Under our current arrangements with Genentech, we are entitled to receive royalties on worldwide sales of RAPTIVA ^® and LUCENTIS ^® . Successful commercialization of these products is subject to a number of risks, including, but not limited to:

17

Table of Contents

According to Genentech, United States sales of RAPTIVA ^® during 2006 were $89.8 million, compared with $79.2 million and $52.4 million during 2005 and 2004, respectively. According to Serono, sales of RAPTIVA ^® outside of the United States during 2006 were $69.9 million, compared with $33.4 million and $3.9 million during 2005 and 2004, respectively. According to Genentech, United States sales of LUCENTIS ^® were $380.0 million and sales outside the United States were $27.0 million during 2006. LUCENTIS ^® sales began on June 30, 2006, upon its approval by regulatory agencies. Given our current reliance on RAPTIVA ^® and LUCENTIS ^® as principal sources of our revenues, any material adverse developments with respect to the commercialization of RAPTIVA ^® or LUCENTIS ^® may cause our revenues to decrease and may cause us to incur losses in the future.

Because our products are still being developed, we will require substantial funds to continue; we cannot be certain that funds will be available and, if they are not available, we may have to take actions which could adversely affect your investment.

If adequate funds are not available, we may have to raise additional funds in a manner that may dilute or otherwise adversely affect the rights of existing shareholders, curtail or cease operations, or file for bankruptcy protection in extreme circumstances. We have spent, and we expect to continue to spend, substantial funds in connection with:

Based on current spending levels, anticipated revenues, collaborator funding, proceeds from our convertible note offerings in February of 2005 and February of 2006, our November 2006 term loan and other sources of funding we believe to be available, we estimate that we have sufficient cash resources to meet our anticipated net cash needs through at least 2008. Any significant revenue shortfalls, increases in planned spending on development programs or more rapid progress of development programs than anticipated, as well as the unavailability of anticipated sources of funding, could shorten this period. Progress or setbacks by potentially competing products may also affect our ability to raise new funding on acceptable terms. As a result, we do not know when or whether:

Cash balances and operating cash flow are influenced primarily by the timing and level of payments by our licensees and development partners, as well as by our operating costs.

18

Table of Contents

Our level of leverage and debt service obligations could adversely affect our financial condition.

As of December 31, 2006, we (including our subsidiaries) had approximately $98.2 million, including our embedded derivative, of indebtedness outstanding. We may not be able to generate cash sufficient to pay the principal of, interest on and other amounts due in respect of our indebtedness when due. We and our subsidiaries may also incur additional debt that may be secured. In connection with our collaboration with Novartis, Novartis has extended a line of credit to us (through our U.S subsidiary) for $50.0 million to fund up to 75% of our expenses thereunder, of which $16.4 million was drawn as of December 31, 2006. This line of credit is secured by a pledge of our interest in the collaboration. On November 9, 2006, XOMA (US) LLC entered into a five-year, $35.0 million term loan facility with Goldman Sachs Specialty Lending Holdings, Inc. (“Goldman Sachs”) and borrowed the full amount thereunder. The loan is guaranteed by XOMA and is secured by the payment rights due to XOMA (US) LLC relating to RAPTIVA ^® , LUCENTIS ^® and CIMZIA ^™ . As a result, these assets will not be available to XOMA or any other lender to secure future indebtedness.

Our level of debt and debt service obligations could have important effects on us and our investors. These effects may include:

Our ability to satisfy our debt obligations will depend upon our future operating performance and the availability of refinancing debt. If we are unable to service our debt and fund our business, we may be forced to reduce or delay capital expenditures, seek additional debt financing or equity capital, restructure or refinance our debt or sell assets. We cannot assure you that we would be able to obtain additional financing, refinance existing debt or sell assets on satisfactory terms or at all.

Most of our therapeutic products have not received regulatory approval. If these products do not receive regulatory approval, neither our third party collaborators nor we will be able to manufacture and market them.

Our products cannot be manufactured and marketed in the United States and other countries without required regulatory approvals. The United States government and governments of other countries extensively regulate many aspects of our products, including:

19

Table of Contents

In the United States, the FDA regulates pharmaceutical products under the Federal Food, Drug, and Cosmetic Act and other laws, including, in the case of biologics, the Public Health Service Act. At the present time, we believe that most of our products will be regulated by the FDA as biologics. Changes in the regulatory approval policy during the development period, changes in, or the enactment of, additional regulations or statutes or changes in regulatory review for each submitted product application may cause delays in the approval or rejection of an application. Even if the FDA or other regulatory agency approves a product candidate, the approval may impose significant restrictions on the indicated uses, conditions for use, labeling, advertising, promotion, marketing and/or production of such product. Even for approved products such as RAPTIVA ^® and LUCENTIS ^® , the FDA may impose ongoing requirements for post-approval studies, including additional research and development and clinical trials, and may subsequently withdraw approval based on these additional trials. The FDA and other agencies also may impose various civil or criminal sanctions for failure to comply with regulatory requirements, including withdrawal of product approval. State regulations may also affect our proposed products. The FDA has substantial discretion in both the product approval process and manufacturing facility approval process and, as a result of this discretion and uncertainties about outcomes of testing, we cannot predict at what point, or whether, the FDA will be satisfied with our or our collaborators’ submissions or whether the FDA will raise questions which may be material and delay or preclude product approval or manufacturing facility approval. As we accumulate additional clinical data, we will submit it to the FDA, which may have a material impact on the FDA product approval process.

We face uncertain results of clinical trials of our potential products.

Our potential products will require significant additional research and development, extensive preclinical studies and clinical trials and regulatory approval prior to any commercial sales. This process is lengthy and expensive, often taking a number of years. As clinical results are frequently susceptible to varying interpretations that may delay, limit or prevent regulatory approvals, the length of time necessary to complete clinical trials and to submit an application for marketing approval for a final decision by a regulatory authority varies significantly. As a result, it is uncertain whether:

For example,

20

Table of Contents

Given that regulatory review is an interactive and continuous process, we maintain a policy of limiting announcements and comments upon the specific details of regulatory review of our products, subject to our obligations under the securities laws, until definitive action is taken.

Because all of our products are still being developed, we have sustained losses in the past and we expect to sustain losses in the future.

We have experienced significant losses and, as of December 31, 2006, we had an accumulated deficit of $727.5 million.

For the year ended December 31, 2006, we had a net loss of approximately $51.8 million or $0.54 per common share (basic and diluted). For the year ended December 31, 2005, as a result of the restructuring of our Genentech arrangement and subsequent extinguishment of our obligation to pay $40.9 million under a development loan and related one-time credit to other income, we had net income of approximately $2.8 million or $0.03 per common share (basic and diluted).

Our ability to achieve profitability is dependent in large part on the success of our development programs, obtaining regulatory approval for our products and entering into new agreements for product development, manufacturing and commercialization, all of which are uncertain. Our ability to fund our ongoing operations is dependent on the foregoing factors and on our ability to secure additional funds. Because our products are still being developed, we do not know whether we will ever achieve sustained profitability or whether cash flow from future operations will be sufficient to meet our needs.

Our agreements with third parties, many of which are significant to our business, expose us to numerous risks.

Our financial resources and our marketing experience and expertise are limited. Consequently, our ability to successfully develop products depends, to a large extent, upon securing the financial resources and/or marketing capabilities of third parties.

21

Table of Contents

Because our collaborators and licensees are independent third parties, they may be subject to different risks than we are and have significant discretion in determining the efforts and resources they will apply. If these collaborators and licensees do not successfully develop and market these products, we may not have the capabilities, resources or rights to do so on our own. We do not know whether our collaborators or licensees will successfully develop and market any of the products that are or may become the subject of one of our collaboration or licensing arrangements. In particular, each of these arrangements provides for either sharing of collaboration expenses, which means that not only we but our collaborators must have sufficient available funds for the collaborations to continue, or funding solely by our collaborators or licensees. In addition, our collaboration with Novartis provides for funding by it in the form of a line of credit to us, and we cannot be certain that Novartis will provide the necessary funds available when we attempt to draw on the line of credit. Furthermore, our contracts with NIAID contain numerous standard terms and conditions provided for in the applicable federal acquisition regulations and customary in many government contracts. Uncertainty exists as to whether we will be able to comply with these terms and conditions in a timely manner, if at all. In addition, given our relative lack of experience in programs under contract with government agencies, we are uncertain as to the extent of NIAID’s demands and the flexibility that will be granted to us in meeting those demands. Lastly, CIMZIA ^™ (CDP870) has not received marketing approval from the FDA or any foreign governmental agency, and therefore we cannot assure you that it will prove to be safe and effective, will be approved for marketing or will be successfully commercialized.

Even when we have a collaborative relationship, other circumstances may prevent it from resulting in successful development of marketable products.

22

Table of Contents

Although we continue to evaluate additional strategic alliances and potential partnerships, we do not know whether or when any such alliances or partnerships will be entered into.

Certain of our technologies are relatively new and are in-licensed from third parties, so our capabilities using them are unproven and subject to additional risks.

We license technologies from third parties. These technologies include but are not limited to phage display technologies licensed to us in connection with our BCE technology licensing program. However, our experience with some of these technologies remains relatively limited and, to varying degrees, we are still dependent on the licensing parties for training and technical support for these technologies. In addition, our use of these technologies is limited by certain contractual provisions in the licenses relating to them and, although we have obtained numerous licenses, intellectual property rights in the area of phage display are particularly complex. If the owners of the patent rights underlying the technologies we license do not properly maintain or enforce those patents, our competitive position and business prospects could be harmed. Our success will depend in part on the ability of our licensors to obtain, maintain and enforce our licensed intellectual property. Our licensors may not successfully prosecute the patent applications to which we have licenses, or our licensors may fail to maintain existing patents. They may determine not to pursue litigation against other companies that are infringing these patents, or they may pursue such litigation less aggressively than we would. Our licensors may also seek to terminate our license, which could cause us to lose the right to use the licensed intellectual property and adversely affect our ability to commercialize our technologies, products or services.

Our share price may be volatile and there may not be an active trading market for our common shares.

There can be no assurance that the market price of our common shares will not decline below its present market price or that there will be an active trading market for our common shares. The market prices of biotechnology companies have been and are likely to continue to be highly volatile. Fluctuations in our operating results and general market conditions for biotechnology stocks could have a significant impact on the volatility of our common share price. We have experienced significant volatility in the price of our common shares. From January 1, 2006 through March 5, 2007, our share price has ranged from a high of $3.50 to a low of $1.57. On March 5, 2007, the closing price of the common shares as reported on the Nasdaq National Market was $2.84 per share. Factors contributing to such volatility include, but are not limited to:

23

Table of Contents

We or our third party collaborators or licensees may not have adequate manufacturing capacity sufficient to meet market demand.

Genentech is responsible for manufacturing or arranging for the manufacturing of commercial quantities of RAPTIVA ^® and LUCENTIS ^® . Should Genentech have difficulty in providing manufacturing capacity to produce these products in sufficient quantities, we do not know whether they will be able to meet market demand. If not, we will not realize revenues from the sales of these products. If any of our other products are approved, because we have never commercially introduced any pharmaceutical products, we do not know whether the capacity of our existing manufacturing facilities can be increased to produce sufficient quantities of our products to meet market demand. Also, if we or our third party collaborators or licensees need additional manufacturing facilities to meet market demand, we cannot predict that we will successfully obtain those facilities because we do not know whether they will be available on acceptable terms. In addition, any manufacturing facilities acquired or used to meet market demand must meet the FDA’s quality assurance guidelines.

We do not know whether there will be, or will continue to be, a viable market for the products in which we have an ownership or royalty interest.

Although RAPTIVA ^® was approved in the United States in October of 2003 and in the European Union in 2004 and LUCENTIS ^® was approved in June of 2006 and in the European Union in January of 2007, their acceptance in the marketplace may not continue. Furthermore, even if other products in which we have an interest receive approval in the future, they may not be accepted in the marketplace. In addition, we or our collaborators or licensees may experience difficulties in launching new products, many of which are novel and based on technologies that are unfamiliar to the healthcare community. We have no assurance that healthcare providers and patients will accept such products, if developed. For example, physicians and/or patients may not accept a product for a particular indication because it has been biologically derived (and not discovered and developed by more traditional means) or if no biologically derived products are currently in widespread use in that indication. Similarly, physicians may not accept a product, such as RAPTIVA ^® or LUCENTIS ^® , if they believe other products to be more effective or are more comfortable prescribing other products. Safety concerns may also arise in the course of on-going clinical trials or patient treatment as a result of adverse events or reactions.

24

Table of Contents

Furthermore, government agencies, as well as private organizations involved in healthcare, from time to time publish guidelines or recommendations to healthcare providers and patients. Such guidelines or recommendations can be very influential and may adversely affect the usage of any products we may develop directly (for example, by recommending a decreased dosage of a product in conjunction with a concomitant therapy or a government entity withdrawing its recommendation to screen blood donations for certain viruses) or indirectly (for example, by recommending a competitive product over our product). Consequently, we do not know if physicians or patients will adopt or use our products for their approved indications.

Products and technologies of other companies may render some or all of our products noncompetitive or obsolete.

Developments by others may render our products or technologies obsolete or uncompetitive. Technologies developed and utilized by the biotechnology and pharmaceutical industries are continuously and substantially changing. Competition in the areas of genetically engineered DNA-based and antibody-based technologies is intense and expected to increase in the future as a number of established biotechnology firms and large chemical and pharmaceutical companies advance in these fields. Many of these competitors may be able to develop products and processes competitive with or superior to our own for many reasons, including that they may have:

These factors may enable others to develop products and processes competitive with or superior to our own or those of our collaborators. In addition, a significant amount of research in biotechnology is being carried out in universities and other non-profit research organizations. These entities are becoming increasingly interested in the commercial value of their work and may become more aggressive in seeking patent protection and licensing arrangements. Furthermore, positive or negative developments in connection with a potentially competing product may have an adverse impact on our ability to raise additional funding on acceptable terms. For example, if another product is perceived to have a competitive advantage, or another product’s failure is perceived to increase the likelihood that our product will fail, then investors may choose not to invest in us on terms we would accept or at all.

Without limiting the foregoing, we are aware that:

25

Table of Contents

In addition to LUCENTIS ^® , there are two other FDA-approved therapies to treat macular degeneration: Pfizer, Inc.’s and OSI Pharmaceuticals, Inc.’s Macugen ^® and Novartis’ and QLT Inc.’s Visudyne ^® . It is also possible that LUCENTIS ^® will compete with Genentech’s cancer drug Avastin ^® .

There are several companies developing topical peptide treatments which may compete with XOMA 629 in acne. Migenix Inc. and its partner Cutanea Life Sciences, Inc. are developing CLS001 (formerly MBI 594AN) for roseasea, a topical peptide that has completed two Phase II trials for the treatment of acne. Helix Biomedix, Inc. is developing several peptide compounds. Medicis Pharmaceutical Corp. has rights to human derived antimicrobial peptides that may be developed for acne.

In collaboration with Novartis, we are co-developing a humanized antibody to the target CD40, and, at the current time, there are several CD40-related programs under development, mostly focused on the development of CD40 ligand products. For example, SGN-40 is a humanized monoclonal antibody under development by Seattle Genetics, Inc. which is targeting CD40 antigen. Seattle Genetics is currently conducting a phase II clinical trial for patients with diffuse large B-cell lymphoma, the most common type of aggressive non-Hodgkin’s lymphoma, and phase I trials for patients with multiple myeloma or chronic lymphocytic leukemia. In January of 2007, Seattle Genetics entered into an exclusive worldwide license agreement with Genentech to develop and commercialize SGN-40. Under the agreement, Genentech will fund future research, development, manufacturing and commercialization costs. In January of 2007, Kirin Brewery Company, Limited and Astellas Pharma Inc. announced that they have entered into a license and collaborative research and development agreement under which they will exclusively collaborate in developing and marketing a fully human anti-CD40 antagonistic monoclonal antibody worldwide with a first target indication of prophylaxis of organ rejection associated with organ transplantation.

It is possible that other companies may be developing other products based on the same human protein as our NEUPREX ^® product, and these products may prove to be more effective than NEUPREX ^® . It is also possible that other companies may be developing other products based on the same therapeutic target as our XOMA 052 product and these products may prove to be more effective than XOMA 052.

26

Table of Contents

Even if we or our third party collaborators or licensees bring products to market, we may be unable to effectively price our products or obtain adequate reimbursement for sales of our products, which would prevent our products from becoming profitable.

If we or our third party collaborators or licensees succeed in bringing our product candidates to the market, they may not be considered cost-effective, and reimbursement to the patient may not be available or may not be sufficient to allow us to sell our products on a competitive basis. In both the United States and elsewhere, sales of medical products and treatments are dependent, in part, on the availability of reimbursement to the patient from third-party payors, such as government and private insurance plans. Third-party payors are increasingly challenging the prices charged for pharmaceutical products and services. Our business is affected by the efforts of government and third-party payors to contain or reduce the cost of health care through various means. In the United States, there have been and will continue to be a number of federal and state proposals to implement government controls on pricing. In addition, the emphasis on managed care in the United States has increased and will continue to increase the pressure on the pricing of pharmaceutical products. We cannot predict whether any legislative or regulatory proposals will be adopted or the effect these proposals or managed care efforts may have on our business.

If we and our partners are unable to protect our intellectual property, in particular our patent protection for our principal products and processes, and prevent its use by third parties, our ability to compete in the market will be harmed, and we may not realize our profit potential.

We rely on patent protection, as well as a combination of copyright, trade secret, and trademark laws to protect our proprietary technology and prevent others from duplicating our products. However, these means may afford only limited protection and may not:

Because of the length of time and the expense associated with bringing new products to the marketplace, we and our partners hold and are in the process of applying for a number of patents in the United States and abroad to protect our products and important processes and also have obtained or have the right to obtain exclusive licenses to certain patents and applications filed by others. However, the mere issuance of a patent is not conclusive as to its validity or its enforceability. The United States Federal Courts or equivalent national courts or patent offices elsewhere may invalidate our patents or find them unenforceable. In addition, the laws of foreign countries may not protect our intellectual property rights effectively or to the same extent as the laws of the United States. If our intellectual property rights are not adequately protected, we may not be able to commercialize our technologies, products, or services, and our competitors could commercialize our technologies, which could result in a decrease in our sales and market share that would harm our business and operating results. Specifically, the patent position of biotechnology companies generally is highly uncertain and involves complex legal and factual questions. The legal standards governing the validity of biotechnology patents are in transition, and current defenses as to issued biotechnology patents may not be adequate in the future. Accordingly, there is uncertainty as to:

27

Table of Contents

We have established an extensive portfolio of patents and applications, both United States and foreign, related to our BPI-related products, including novel compositions, their manufacture, formulation, assay and use. We have also established a portfolio of patents, both United States and foreign, related to our BCE technology, including claims to novel promoter sequences, secretion signal sequences, compositions and methods for expression and secretion of recombinant proteins from bacteria, including immunoglobulin gene products.

If certain patents issued to others are upheld or if certain patent applications filed by others issue and are upheld, we may require licenses from others in order to develop and commercialize certain potential products incorporating our technology or we may become involved in litigation to determine the proprietary rights of others. These licenses, if required, may not be available on acceptable terms, and any such litigation may be costly and may have other adverse effects on our business, such as inhibiting our ability to compete in the marketplace and absorbing significant management time.

Due to the uncertainties regarding biotechnology patents, we also have relied and will continue to rely upon trade secrets, know-how and continuing technological advancement to develop and maintain our competitive position. All of our employees have signed confidentiality agreements under which they have agreed not to use or disclose any of our proprietary information. Research and development contracts and relationships between us and our scientific consultants and potential customers provide access to aspects of our know-how that are protected generally under confidentiality agreements. These confidentiality agreements may be breached or may not be enforced by a court. To the extent proprietary information is divulged to competitors or to the public generally, such disclosure may adversely affect our ability to develop or commercialize our products by giving others a competitive advantage or by undermining our patent position.

Litigation regarding intellectual property can be costly and expose us to risks of counterclaims against us.

We may be required to engage in litigation or other proceedings to protect our intellectual property. The cost to us of this litigation, even if resolved in our favor, could be substantial. Such litigation could also divert management’s attention and resources. In addition, if this litigation is resolved against us, our patents may be declared invalid, and we could be held liable for significant damages. In addition, we may be subject to a claim that we are infringing another party’s patent. If such claim is resolved against us, we or our collaborators may be enjoined from developing, manufacturing, selling or importing products, processes or services unless we obtain a license from the other party. Such license may not be available on reasonable terms, thus preventing us from using these products, processes or services and adversely affecting our revenue.

Manufacturing risks and inefficiencies may adversely affect our ability to manufacture products for ourselves or others.

We are subject to manufacturing risks which may hinder our ability to provide manufacturing services for our own benefit or to third parties. Additionally, unanticipated fluctuations in customer requirements may lead to manufacturing inefficiencies. We must provide our manufacturing services in compliance with regulatory requirements, in sufficient quantities and on a timely basis, while maintaining acceptable product quality and manufacturing costs. Additional resources and changes in our manufacturing processes may be required for each new product or customer or to meet increasing customer requirements once a contract has been initiated, and this work may not be successfully or efficiently completed.

In addition, the development work and products addressed in new contracts may not share production attributes with our existing projects to the extent we anticipate, and consequently these new contracts may require the development of new manufacturing technologies and expertise. If we are unable to develop manufacturing capabilities as needed, on acceptable terms, our ability to complete these contracts or enter into additional contracts may be adversely affected.

Manufacturing and quality problems may arise in the future as we continue to perform these services for our own benefit and under additional manufacturing contracts. Consequently, our internal development goals or

28

Table of Contents

milestones under our contracts may not be achieved in a timely manner or at a commercially reasonable cost, or at all. In addition, we continue to make investments to improve our manufacturing processes and to design, develop and purchase manufacturing equipment that may not yield the improvements that we expect. Inefficiencies or constraints related to our manufacturing may adversely affect our overall financial results. Such inefficiencies or constraints may also result in delays or loss of current or potential customers due to their dissatisfaction.

The financial terms of future collaborative or licensing arrangements could result in dilution of our share value.

Funding from collaboration partners and others has in the past and may in the future involve issuance by us of our shares. Because we do not currently have any such arrangements, we cannot be certain how the purchase price of such shares, the relevant market price or premium, if any, will be determined or when such determinations will be made. Any such issuance could result in dilution in the value of our issued and outstanding shares.

Because many of the companies we do business with are also in the biotechnology sector, the volatility of that sector can affect us indirectly as well as directly.

As a biotechnology company that collaborates with other biotech companies, the same factors that affect us directly can also adversely impact us indirectly by affecting the ability of our collaborators, partners and others we do business with to meet their obligations to us and reduce our ability to realize the value of the consideration provided to us by these other companies.

For example, in connection with our licensing transactions relating to our BCE technology, we have in the past and may in the future agree to accept equity securities of the licensee in payment of license fees. The future value of these or any other shares we receive is subject both to market risks affecting our ability to realize the value of these shares and more generally to the business and other risks to which the issuer of these shares may be subject.

As we do more business internationally, we will be subject to additional political, economic and regulatory uncertainties.

We may not be able to successfully operate in any foreign market. We believe that, because the pharmaceutical industry is global in nature, international activities will be a significant part of our future business activities and that, when and if we are able to generate income, a substantial portion of that income will be derived from product sales and other activities outside the United States. Foreign regulatory agencies often establish standards different from those in the United States, and an inability to obtain foreign regulatory approvals on a timely basis could put us at a competitive disadvantage or make it uneconomical to proceed with a product’s development. International operations and sales may be limited or disrupted by:

29

Table of Contents

Because we are a relatively small biopharmaceutical company with limited resources, we may not be able to attract and retain qualified personnel, and the loss of key personnel could delay or prevent achieving our objectives.

Our success in developing marketable products and achieving a competitive position will depend, in part, on our ability to attract and retain qualified scientific and management personnel, particularly in areas requiring specific technical, scientific or medical expertise. There is intense competition for such personnel. Our research, product development and business efforts could be adversely affected by the loss of one or more key members of our scientific or management staff, particularly our executive officers: John L. Castello, our Chairman of the Board, President and Chief Executive Officer; J. David Boyle II, our Vice President, Finance and Chief Financial Officer; Patrick J. Scannon, M.D., Ph.D., our Executive Vice President and Chief Biotechnology Officer; and Christopher J. Margolin, our Vice President, General Counsel and Secretary. We currently have no key person insurance on any of our employees. In February of 2007, Mr. Castello announced his plans to retire. Although he intends to continue to serve in his present capacities during the candidate search and transition period, our business could be adversely affected if the search and transition period take longer than expected or we are unable to find a suitable replacement.

We had approximately 256 employees as of December 31, 2006, and we anticipate that we will require additional experienced executive, accounting, research and development, legal, administrative and other personnel in the future. There is intense competition for the services of these personnel, especially in California. Moreover, we expect that the high cost of living in the San Francisco Bay Area, where our headquarters and manufacturing facilities are located, may impair our ability to attract and retain employees in the future. If we do not succeed in attracting new personnel and retaining and motivating existing personnel, our operations may suffer and we may be unable to implement our current initiatives or grow effectively.

Calamities, power shortages or power interruptions at our Berkeley headquarters and manufacturing facility could disrupt our business and adversely affect our operations, and could disrupt the businesses of our customers.

Our principal operations are located in Northern California, including our corporate headquarters and manufacturing facility in Berkeley, California. In addition, many of our collaborators and licensees are located in California. All of these locations are in areas of seismic activity near active earthquake faults. Any earthquake, terrorist attack, fire, power shortage or other calamity affecting our facilities or our customers’ facilities may disrupt our business and could have material adverse effect on our business and results of operations.

We are exposed to an increased risk of product liability claims.

The testing, marketing and sales of medical products entails an inherent risk of allegations of product liability. In the event of one or more large, unforeseen awards of damages against us, our product liability insurance may not provide adequate coverage. A significant product liability claim for which we were not covered by insurance would have to be paid from cash or other assets. To the extent we have sufficient insurance coverage, such a claim would result in higher subsequent insurance rates. In addition, product liability claims can have various other ramifications including loss of future sales opportunities, increased costs associated with replacing products, and a negative impact on our goodwill and reputation, which could also adversely affect our business and operating results.

We may be subject to increased risks because we are a Bermuda company.

Alleged abuses by certain companies that have changed their legal domicile from jurisdictions within the United States to Bermuda have created an environment where, notwithstanding that we changed our legal domicile in a transaction that was approved by our shareholders and fully taxable to our company under United States law, we may be exposed to various prejudicial actions, including:

30

Table of Contents

We do not know whether any of these things will happen, but if implemented one or more of them may have an adverse impact on our future operations or our share price.

If you were to obtain a judgment against us, it may be difficult to enforce against us because we are a foreign entity.

We are a Bermuda company. All or a substantial portion of our assets, including substantially all of our intellectual property, may be located outside the United States. As a result, it may be difficult for shareholders and others to enforce in United States courts judgments obtained against us. We have irrevocably agreed that we may be served with process with respect to actions based on offers and sales of securities made hereby in the United States by serving Christopher J. Margolin, c/o XOMA Ltd., 2910 Seventh Street, Berkeley, California 94710, our United States agent appointed for that purpose. Uncertainty exists as to whether Bermuda courts would enforce judgments of United States courts obtained in actions against us or our directors and officers that are predicated upon the civil liability provisions of the United States securities laws or entertain original actions brought in Bermuda against us or such persons predicated upon the United States securities laws. There is no treaty in effect between the United States and Bermuda providing for such enforcement, and there are grounds upon which Bermuda courts may not enforce judgments of United States courts. Certain remedies available under the United States federal securities laws may not be allowed in Bermuda courts as contrary to that nation’s policy.

Our shareholder rights agreement or bye-laws may prevent transactions that could be beneficial to our shareholders and may insulate our management from removal.

In February of 2003, we adopted a new shareholder rights agreement (to replace the shareholder rights agreement that had expired), which could make it considerably more difficult or costly for a person or group to acquire control of us in a transaction that our board of directors opposes.

Our bye-laws:

These provisions of our shareholders rights agreement and our bye-laws, alone or in combination with each other, may discourage transactions involving actual or potential changes of control, including transactions that otherwise could involve payment of a premium over prevailing market prices to holders of common shares, could limit the ability of shareholders to approve transactions that they may deem to be in their best interests, and could make it considerably more difficult for a potential acquirer to replace management.

We may issue additional equity securities and thereby materially and adversely affect the price of our common shares.

We are authorized to issue, without shareholder approval, 1,000,000 preference shares, of which 2,959 were issued and outstanding as of December 31, 2006, which may give other shareholders dividend, conversion,

31

Table of Contents

voting, and liquidation rights, among other rights, which may be superior to the rights of holders of our common shares. In addition, we are authorized to issue, without shareholder approval, up to 210,000,000 common shares, of which 105,454,389 were issued and outstanding as of December 31, 2006. If we issue additional equity securities, the price of our common shares and, in turn, the price of our convertible notes may be materially and adversely affected. In addition, as of December 31, 2006, there were $44.5 million aggregate principal amount of New Notes outstanding, which were convertible into an aggregate of 23,750,873 common shares, with an aggregate of 1,889,317 additional shares issuable in lieu of the additional interest that would be due on such conversion.

If the trading price of our common shares fails to comply with the continued listing requirements of The Nasdaq National Market, we would face possible delisting, which would result in a limited public market for our common shares and make obtaining future debt or equity financing more difficult for us.

If we do not continue to comply with the continued listing requirements for The Nasdaq National Market, then Nasdaq may provide written notification regarding the delisting of our securities. At that time, we would have the right to request a hearing to appeal The Nasdaq determination and would also have the option to apply to transfer our securities to The Nasdaq SmallCap Market.

We cannot be sure that our price will comply with the requirements for continued listing of our common shares on The Nasdaq National Market, or that any appeal of a decision to delist our common shares will be successful. If our common shares lose their status on The Nasdaq National Market and we are not successful in obtaining a listing on The Nasdaq SmallCap Market, our common shares would likely trade in the over-the-counter market.

If our common shares are neither listed for trading on a United States national or regional securities exchange nor approved for trading on The Nasdaq National Market, Nasdaq SmallCap Market or any other established United States system of automated dissemination or quotations of securities prices, it would be deemed a “fundamental change” under the indenture governing our convertible notes, giving the holders thereof the right to require us to repurchase such notes. Our failure to repurchase our convertible notes would constitute an event of default under the notes indenture, which might constitute an event of default under the terms of our other debt.

If our shares were to trade on the over-the-counter market, selling our common shares could be more difficult because smaller quantities of shares would likely be bought and sold, transactions could be delayed, and security analysts’ coverage of us may be reduced. In addition, in the event our common shares are delisted, broker-dealers have certain regulatory burdens imposed upon them, which may discourage broker-dealers from effecting transactions in our common shares, further limiting the liquidity thereof. These factors could result in lower prices and larger spreads in the bid and ask prices for common shares.

Such delisting from The Nasdaq National Market or future declines in our share price could also greatly impair our ability to raise additional necessary capital through equity or debt financing, and could significantly increase the ownership dilution to shareholders caused by our issuing equity in financing or other transactions. Consent under the Exchange Control Act 1972 (and its related regulations) has been obtained from the Bermuda Monetary Authority for the issue and transfer of our shares, notes and other securities to and between non-residents of Bermuda for exchange control purposes, but this consent is conditional on our shares remaining listed on an appointed stock exchange. We cannot assure you that the Bermuda Monetary Authority will give the same or a similar consent in the event our common shares are no longer listed on The Nasdaq National Market or another appointed stock exchange. In the absence of such a general consent, specific consents of the Bermuda Monetary Authority would be required for certain issues and transfers of our shares, notes and other securities.

None.

32

Table of Contents