Gilead Licenses Rights Under Its Selex and Aptamer Patent Estate to Archemix

Foster City, CA; and Cambridge, MA -- October 23, 2001

Gilead Sciences, Inc. (Nasdaq: GILD) announced today that it has out-licensed its previously unlicensed intellectual property rights under the SELEX™ (Systemic Evolution of Ligands through EXponential Enrichment) process patent estate to Cambridge, MA-based Archemix Corporation.

Gilead will receive $17.5 million in cash, $9.0 million in 2001 and $8.5 million in 2002. Additionally, Gilead will receive warrants in Archemix.

The agreement with Archemix provides exclusive rights to the SELEX process, including therapeutic and other commercial applications to the extent not already licensed under pre-existing agreements. Aptamers are three-dimensional oligonucleotides made through the SELEX process that bind to molecular targets in a manner conceptually similar to antibodies. Aptamers, like antibodies, have potential in a broad range of applications including therapeutic drug discovery and target validation.

"The very broad SELEX patent estate significantly expands the scope of our discovery platform," said Martin Stanton, Ph.D., Archemix Founder and President. "Archemix is now positioned to use the complete array of selection technologies to accelerate all steps in the drug discovery process. We recognize that other companies have an interest in the SELEX technology and are looking forward to establishing productive partnerships to enable applications outside our core business."

Gilead Sciences will retain a non-exclusive right to utilize this technology for internal research purposes.

"This deal is another important step for Gilead as we continue to focus solidly on our core competencies," said John Martin, Ph.D., President and Chief Executive Officer of Gilead Sciences. "Because of their expertise in the field of oligonucleotides, Archemix is poised to maximize the potential of this technology."

About Archemix
Archemix Corporation (www.archemix.com), a privately held company located in Cambridge, Massachusetts, is developing the RiboReporterTM platform to integrate all steps in drug discovery. RiboReporters are molecular sensors created through the process of in vitro evolution and can be used to build unique molecular profiling arrays that enable proteomic and metabolomic analysis. RiboReporter-based cellular assays make it possible to follow proteins, metabolites, and drugs in real time in live cells.

About Gilead Sciences
Gilead Sciences, Inc., headquartered in Foster City, CA, is an independent biopharmaceutical company that seeks to provide accelerated solutions for patients and the people who care for them. Gilead discovers, develops, manufactures and commercializes proprietary therapeutics for challenging infectious diseases (viral, fungal and bacterial infections) and cancer. Gilead maintains research, development or manufacturing facilities in the United States, Europe and Australia. For more information on Gilead Sciences, please visit the company's Web site at www.gilead.com or call the Gilead Corporate Communications Department at 1-800-GILEAD-5 (1-800-445-3235).

SELEX is a trademark of Gilead Sciences, Inc.