Gilead Sciences Announces Commencement of Topical Ophthalmic Cidofovir Clinical Study by Storz.

Sciences, Inc. (Nasdaq: GILD) announced today that its collaborative partner Storz Instrument Company has commenced a Phase I human clinical study of topical ophthalmic cidofovir.

This study is designed to determine the safety and pharmacokinetics of topical ophthalmic cidofovir, an eye-drop formulation that is in development for the potential treatment of a variety of viruses that can cause external infections of the eye.

The clinical trial program is being conducted by Storz, the ophthalmology product subsidiary of American Home Products Corporation, to whom Gilead licensed worldwide marketing rights for the eye-drop formulation of cidofovir in August 1994. Under the terms of the agreement with Storz, Gilead supplies the bulk drug and is entitled to receive license fees, milestone payments and royalties on product sales.

Viral infections of the external eye are among the most common conditions seen in clinical practice by family practitioners, internists, pediatricians, optometrists and ophthalmologists. Cidofovir is a broad-spectrum antiviral compound that has been shown to be active against all three of the viral pathogens that cause the majority of viral infections of the outer eye: herpes simplex virus (HSV), varicella zoster virus (VZV) and adenovirus.

Herpes keratitis, caused by HSV, is a serious infection of the cornea on the outer surface of the eye and is the leading cause of infectious blindness in the United States and one of the leading causes of infectious blindness worldwide. Adenovirus is the leading cause of infectious "pinkeye," a highly contagious disease in adults and children, which can result in lost days of school and work. Currently, there is no effective antiviral therapy to control adenoviral infections in the eye, and thus there is no ophthalmic product approved for broad-spectrum antiviral use.

Cidofovir is one of several small molecule compounds in development at Gilead Sciences from a new class of antiviral compounds known as nucleotide analogues. Gilead retains worldwide rights to all formulations of cidofovir other than the topical ophthalmic eye-drop version licensed to Storz.

Gilead is also pursuing independently multiple clinical programs based upon the broad-spectrum antiviral activity of cidofovir. These programs include formulations of cidofovir for the potential treatment of cytomegalovirus (CMV) retinitis, which if untreated leads to loss of vision over time in patients with AIDS. Gilead also has product candidates in clinical studies for viral diseases caused by the human immunodeficiency virus (HIV), human papillomavirus, herpes simplex virus and hepatitis B virus.

Gilead Sciences, based in Foster City, California, is a leader in the discovery and development of a new class of human therapeutics based on nucleotides, the building blocks of DNA and RNA. The Company's research and development efforts encompass three interrelated programs: small molecule antivirals, cardiovascular therapeutics and genetic code blockers for cancer and other diseases.

Gilead's expertise in each of these areas has also resulted in the discovery of non-nucleotide product candidates that expand the Company's technology platforms. Gilead common stock is traded on The Nasdaq Stock Market under the symbol GILD.

American Home Products is one of the world's largest research-based pharmaceutical and health care products companies and is a leading developer, manufacturer and marketer of prescription drugs and over-the-counter medications. It is also a leader in women's health products, vaccines, generic pharmaceuticals, biotechnology, agricultural products, animal health care, medical devices, infant nutritionals and food products. -0- Note to Editors: Additional written materials and recent releases are available through the Gilead Fax-On-Demand Information Service by dialing 800/276-7318.

CONTACT: Gilead Sciences Inc.

Lana Lauher, 415/573-4858