FREMONT, CALIF., December 1, 1999 - Abgenix, Inc. (Nasdaq: ABGX) today announced that it has signed a research license and option agreement with Chiron, Inc. ("Chiron") (Nasdaq: CHIR) under which Chiron will use Abgenix's XenoMouse™ technology to generate fully human monoclonal antibodies to an undisclosed antigen in the field of autoimmune diseases. In return, Abgenix will receive a technology access payment and could receive additional fees and milestone payments plus royalties on future product sales by Chiron. Under a separate research collaboration agreement, Chiron may use XenoMouse to generate fully human monoclonal antibodies on up to four cancer targets. Chiron will be responsible for product development, manufacturing, and marketing of any products developed through the collaboration.

"We are delighted to be working with Chiron, one of the world's leading biotechnology companies," stated R. Scott Greer, president and CEO of Abgenix. "Chiron becomes the fourteenth partner using our XenoMouse technology to generate antibody product candidates. This deal also represents the eighth new potential product candidate being pursued by one of our XenoMouse collaborators this year."

Abgenix is a biopharmaceutical company that develops and intends to commercialize antibody therapies for the treatment of such conditions as transplant-related diseases, inflammatory and autoimmune disorders, cardiovascular disease and cancer. Abgenix developed XenoMouse technology to enable the rapid generation of high affinity, fully human antibody product candidates to essentially any disease target appropriate for antibody therapy. Abgenix has collaborative arrangements with multiple pharmaceutical and biotechnology companies involving its XenoMouse technology. In addition, Abgenix has multiple proprietary antibody product candidates under development internally, three of which are in human clinical trials.

Statements made in this press release about Abgenix's XenoMouse technology, product development activities and collaborative arrangements other than statements of historical fact, are forward looking statements and are subject to a number of uncertainties that could cause actual results to differ materially from the statements made, including risks associated with the success of clinical trials, the progress of research and product development programs, the regulatory approval process, competitive products, future capital requirements and the extent and breadth of Abgenix's patent portfolio. Please see Abgenix's public filings with the Securities and Exchange Commission for information about risks that may affect Abgenix.

Contact:
Kurt Leutzinger
Vice President and
Chief Financial Officer
Abgenix Inc.
510-608-6575

Marion E. Glick
Porter Novelli
212-601-8273