Phase III Study Evaluating Gilead's Viread(R) for the Treatment of Chronic Hepatitis B Virus Meets Primary Endpoint

Gilead Sciences, Inc. (Nasdaq:GILD) today announced that Study
102, a Phase III clinical trial evaluating the company's once-daily
anti-HIV drug Viread(R) (tenofovir disoproxil fumarate or tenofovir
DF) 300 mg as a potential treatment for chronic hepatitis B virus
(HBV) infection, met its primary efficacy endpoint. The study shows
that Viread is non-inferior to the company's once-daily antiviral drug
Hepsera(R) (adefovir dipivoxil) among patients with
HBeAg-negative/anti-HBe positive (presumed pre-core mutant) chronic
HBV infection. The primary efficacy endpoint, the proportion of
patients with a complete response at week 48, was defined by serum HBV
DNA levels below 400 copies/mL and histologic improvement
characterized by at least a two point reduction in the Knodell
necroinflammatory score (a measure of necro-inflammation - an
inflammatory process in the liver including or leading to death of
liver cells) with no concurrent worsening of fibrosis (scarring of
liver tissue).

At 48 weeks, 70.8 percent of patients in the Viread arm (n=250)
had a complete response compared to 48.8 percent in the Hepsera arm
(n=125; p less than 0.001). The most commonly observed
treatment-emergent adverse events of moderate intensity or higher were
abdominal pain, back pain, headache, respiratory infections,
creatinine phosphokinase and transaminase elevations. The incidence of
these events was comparable between the Viread and Hepsera arms of the
study. In addition, the incidence of grade 3 or 4 laboratory
abnormalities was comparable between the two arms. Full study results
will be submitted for presentation at an upcoming scientific meeting.

"Chronic hepatitis B remains a serious disease that impacts more
than one million people in the United States and an estimated 400
million people worldwide," said Franck Rousseau, MD, Vice President,
Clinical Research, Gilead Sciences. "We believe Viread has the
potential to be an important treatment option for patients with
chronic hepatitis B and look forward to sharing detailed data from
this study at a scientific conference later this year."

Study 102 is one of two Phase III pivotal studies evaluating the
efficacy, safety and tolerability of Viread for the treatment of
chronic hepatitis B. The second study (Study 103), a 48-week trial
among patients with hepatitis B "e" antigen (HBeAg)-positive chronic
hepatitis B, is expected to be complete later this year.

The active ingredient in Viread, tenofovir DF, is currently the
most prescribed molecule in the United States for combination HIV
therapy. Viread received approval as an anti-HIV medication from the
U.S. Food and Drug Administration (FDA) in October 2001 and from the
European Commission in February 2002. Viread is not approved as a
treatment for chronic hepatitis B, and data from this analysis have
not been reviewed by the FDA.

Study Design

Study 102 is a multi-center, randomized, double-blind Phase III
clinical trial that compares the efficacy, safety and tolerability of
Viread and Hepsera over 48-weeks among patients with
HBeAg-negative/anti-HBe positive (presumed pre-core mutant) chronic
hepatitis B. Three hundred and seventy-five patients were randomized
in a 2:1 ratio to receive either tenofovir DF (300 mg once daily;
n=250) or Hepsera (10 mg once daily; n=125).

About Viread (tenofovir disoproxil fumarate)

In the United States, Viread is indicated in combination with
other antiretroviral agents for the treatment of HIV-1 infection.
Viread should not be used in combination with the fixed-dose
combination products Truvada(R) or Atripla(TM) because they already
contain Viread.

Lactic acidosis and severe hepatomegaly with steatosis, including
fatal cases, have been reported with the use of nucleoside analogues
alone or in combination with other antiretrovirals. Viread is not
approved for the treatment of chronic hepatitis B and the safety and
efficacy of Viread have not been established in patients coinfected
with HBV and HIV. Severe acute exacerbations of hepatitis B have been
reported in patients who have discontinued Viread. Hepatic function
should be monitored closely with both clinical and laboratory
follow-up for at least several months in patients who are co-infected
with HIV and HBV and discontinue Viread. If appropriate, initiation of
anti-hepatitis B therapy may be warranted.

Renal impairment, including cases of acute renal failure and
Fanconi syndrome, has been reported in association with the use of
Viread. It is recommended that creatinine clearance be calculated in
all patients prior to initiating therapy with Viread and as clinically
appropriate during therapy. Coadministration of Viread and didanosine
should be undertaken with caution. Patients should be monitored
closely for didanosine-associated adverse events, and didanosine
should be discontinued if these occur. Patients on atazanavir and
lopinavir/ritonavir plus Viread should be monitored for
Viread-associated adverse events, and Viread should be discontinued if
these occur. When co-administered with Viread, it is recommended that
atazanavir 300 mg be given with ritonavir 100 mg. Atazanavir without
ritonavir should not be co-administered with Viread.

Decreases in bone mineral density (BMD) at the lumbar spine and
hip have been seen with the use of Viread. The effects of
Viread-associated changes in BMD and biochemical markers on long-term
bone health and future fracture risk are unknown. Changes in body fat
have been observed in patients taking anti-HIV medicines. The cause
and long-term health effect of these changes are unknown. Immune
Reconstitution Syndrome has been reported in patients treated with
combination therapy, including Viread.

The most common adverse events among patients receiving Viread
with other antiretroviral agents in a pivotal clinical study (Study
903) were mild to moderate gastrointestinal events and dizziness.
Moderate to severe adverse events occurring in more than 5 percent of
patients receiving Viread included rash (rash, pruritis, maculopapular
rash, urticaria, vesiculobullous rash and pustular rash), headache,
pain, diarrhea, depression, back pain, fever, nausea, abdominal pain,
asthenia (weakness) and anxiety. In another pivotal study (Study 907),
less than 1 percent of patients discontinued participation because of
gastrointestinal events.

It is important for patients to be aware that anti-HIV medicines
including Viread do not cure HIV infection or AIDS and do not reduce
the risk of transmitting HIV to others. Full prescribing information
is available at www.GileadHIV.com.

The parent compound of Viread was discovered through a
collaborative research effort between Dr. Antonin Holy, Institute for
Organic Chemistry and Biochemistry, Academy of Sciences of the Czech
Republic (IOCB) in Prague and Dr. Erik DeClercq, Rega Institute for
Medical Research, Katholic University in Leuven, Belgium.

About Hepsera

Hepsera, a nucleotide analogue for the treatment of chronic
hepatitis B, works by inhibiting HBV DNA polymerase, an enzyme
involved in the replication of the virus in the body.

In the United States, Hepsera is indicated for the treatment of
chronic hepatitis B in adults with evidence of active viral
replication and either evidence of persistent elevations in serum
aminotransferases (ALT or AST) or histologically active disease.

The adverse reactions considered at least possibly related to
treatment reported in 3 percent or greater of patients in the first 48
weeks in Hepsera pivotal clinical studies were asthenia, headache,
abdominal pain, nausea, flatulence, diarrhea and dyspepsia. With
extended treatment, mild to moderate increases in serum creatinine
were observed uncommonly in patients with chronic hepatitis B and
compensated liver disease treated with Hepsera for a median of 49
weeks up to a maximum of 240 weeks. Changes in serum creatinine were
observed very commonly in patients pre- and post-transplantation with
lamivudine-resistant liver disease and multiple risk factors for
changes in renal function who were treated with Hepsera for up to 129
weeks, with a median time on treatment of 19 and 56 weeks,
respectively. Clinical and laboratory evidence of exacerbations of
hepatitis have occurred after discontinuation of treatment with
antiviral therapies for hepatitis B, including Hepsera. Special
warnings and precautions for use are included in the package insert
regarding monitoring of renal function, post-treatment exacerbations
of hepatitis, and the occurrence of lactic acidosis and severe
hepatomegaly with steatosis. Dosing instructions for patients with
underlying renal impairment and for patients co-infected with HIV are
also provided in the package insert, which is available for download
online at www.hepsera.com.

About Gilead Sciences

Gilead Sciences is a biopharmaceutical company that discovers,
develops and commercializes innovative therapeutics in areas of unmet
medical need. The company's mission is to advance the care of patients
suffering from life-threatening diseases worldwide. Headquartered in
Foster City, California, Gilead has operations in North America,
Europe and Australia. For more information on Gilead Sciences, please
visit the company's website at www.gilead.com or call Gilead Public
Affairs at 1-800-GILEAD-5 or 1-650-574-3000.

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, including risks
related to Gilead's ability to successfully commercialize tenofovir DF
for chronic hepatitis B. For example, the FDA may not approve
tenofovir DF for the treatment of chronic hepatitis B in the United
States, and marketing approval, if granted, may have significant
limitations on its use. In addition, future discussions with the FDA
may impact the amount of data needed and timelines for review, which
may differ materially from Gilead's current projections. Further,
safety and efficacy data from additional clinical studies may not
warrant further development of this compound for the treatment of
chronic hepatitis B and completing our clinical studies may take
longer or cost more than expected. In addition, feedback from
regulatory authorities or results from clinical trials might require
modifications or delays in later stage clinical trials or additional
trials to be performed. Further, other regulatory authorities may not
approve tenofovir DF for the treatment of chronic hepatitis B, and
marketing approval, if granted, may have significant limitations on
its use and physicians and may not see advantages of tenofovir DF over
other treatment options and may therefore be reluctant to prescribe
tenofovir DF for chronic hepatitis B. These risks, uncertainties and
other factors could cause actual results to differ materially from
those referred to in the forward-looking statements. The reader is
cautioned not to rely on these forward-looking statements. These and
other risks are described in detail in Gilead's Annual Report on Form
10-K for the year ended December 31, 2006 and its Quarterly Report on
Form 10-Q for the first quarter of 2007, filed with the U.S.
Securities and Exchange Commission. All forward-looking statements are
based on information currently available to Gilead, and Gilead assumes
no obligation to update any such forward-looking statements.

Hepsera and Viread are registered trademarks of Gilead Sciences,
Inc.

For more information on Gilead, please call the Gilead Public
Affairs Department at 1-800-GILEAD-5 (1-800-445-3235) or visit
www.gilead.com.