Gilead Begins Phase I Study of GS7836, an Investigational Anticancer Drug

Foster City, CA -- November 13, 2001

Gilead Sciences, Inc. (Nasdaq: GILD) today announced that it has initiated the first Phase I clinical trial of GS7836, a novel anticancer nucleoside analogue, in Canada. In September 2001, the Canadian Therapeutics Products Directorate (TPD) approved Gilead’s Investigational New Drug Application for GS7836. Gilead plans to initiate additional Phase I trials of GS7836 in other countries in the coming months.

“Our oncology team has advanced GS7836 from a preclinical compound to Phase I trials in just under one year,” said John C. Martin, Ph.D., President and Chief Executive Officer, Gilead Sciences. “This achievement, along with the continued advancement of our lead oncology agent NX211 (liposomal lurtotecan) in several Phase II trials for various cancers, demonstrates the continuing advancement of our oncology franchise.”

Study Design
Conducted in collaboration with the National Cancer Institute Canada – Clinical Trials Group, this initial trial is designed to evaluate the safety, tolerability and toxicity of GS7836 in up to 40 patients at two sites. The study will enroll patients with a variety of solid tumors refractory to standard therapy or for which no curative therapy exists. In this first Phase I trial, the dose of GS7836 will be escalated in successive cohorts of patients to determine the maximum tolerated and recommended Phase II doses.

GS7836
Gilead licensed GS7836 (4’-thio-araC) from Southern Research Institute (SRI) in December 2000. Under the terms of the agreement, Gilead acquired exclusive, worldwide development and commercialization rights to the compound.

GS7836 is a nucleoside analogue and belongs to the same class of compounds as the anticancer agents cytarabine (Cytosar-U®, Pharmacia) and gemcitabine (Gemzar®, Eli Lilly). Cytarabine (commonly known as araC) is approved for the treatment of patients with acute leukemia. Gemcitabine is approved as first-line therapy for patients with pancreatic cancer and in combination therapy for non-small cell lung cancer. Similar to gemcitabine, but unlike araC, GS7836 has demonstrated potent activity against a variety of solid tumors in preclinical experiments performed by both Gilead and SRI. Nucleoside analogues are believed to inhibit tumor growth by preventing the replication of DNA in rapidly growing cancer cells.

Gilead's Oncology Portfolio
Gilead's most advanced product candidate in oncology, NX211, is a proprietary liposomal formulation of the anticancer agent lurtotecan and is currently in Phase II clinical trials. In December 2000, Gilead licensed a thymidylate synthase inhibitor from Glaxo Wellcome (now GlaxoSmithKline) and developed it into the liposomal compound GS7904L, with the goal of enhancing its anti-tumor activity. Gilead plans to initiate Phase I clinical trials of this compound in the near future.

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, manufacturing or sales and marketing facilities in the United States, Europe and Australia.

This press release includes forward-looking statements, within the meaning of the Private Securities Litigation Reform Act of 1995, that are subject to risks, uncertainties and other factors that could cause actual results to differ materially from those referred to in the forward-looking statements, particularly the risks associated with safety, efficacy and development timelines for an investigational compound, and the risk that the Phase I studies of GS7836 will not demonstrate a dose that is suitable for Phase II clinical trials. Actual results could differ materially from those projected in this release. The reader is cautioned not to rely on these forward-looking statements. These and other risks are described in detail in the Gilead Annual Report on Form 10-K for the year ended December 31, 1999 and in Gilead’s Quarterly Reports on Form 10-Q, all of which are on file with the U.S. Securities and Exchange Commission.

For more information on Gilead Sciences, please call the Gilead Corporate Communications Department at 1-800-GILEAD-5 (1-800-445-3235) or visit the corporate Web site at www.gilead.com.