PRINCETON, New Jersey, September 10 /PRNewswire/ --

-R7128 Demonstrates Safety and Tolerability with No Clinically
Significant Adverse Events-

-Conference Call Scheduled for 8:30AM (ET) Today-

Pharmasset, Inc. (Nasdaq: VRUS) is presenting safety, tolerability,
pharmacokinetic and food effect data following single ascending doses of
R7128 at the 14th International Symposium on Hepatitis C Virus and Related
Viruses being held from September 9-13, 2007 in Glasgow, Scotland. R7128 is a
prodrug of PSI-6130, an oral cytidine nucleoside analog polymerase inhibitor
of hepatitis C virus (HCV) that is being developed through Pharmasset's
collaboration with Roche. The poster presentation from the conference is
available in the "Events and Presentations" section of the Investor Center on
Pharmasset's website at www.pharmasset.com.

The Phase 1 single ascending dose study of R7128 was designed to assess
the safety, tolerability and pharmacokinetics of R7128 following single
ascending doses under fasting conditions. The secondary objective of this
study was to explore the effect of food on the pharmacokinetics of R7128.
Single oral doses of R7128 were administered to 46 healthy volunteers in five
sequential dose groups (500 mg, 1500 mg, 4500 mg, 6000 mg, and 9000 mg) and
one food effect group (1500 mg). There were 8 subjects per sequential dose
group (6 active, 2 placebo) and 6 subjects in the food effect group (all
active).

Nineteen adverse events (AEs) were reported during the study, including
headache, sunburn, sore throat and nasal congestion. All AEs were mild to
moderate, none were related to dose and no gastrointestinal AEs were
observed. There were no clinically significant changes in vital signs,
electrocardiograms, hematologic, renal or other laboratory parameters. The
plasma exposure to PSI-6130 and PSI-6206, the uridine metabolite of PSI-6130,
increased with increasing doses of R7128. Food increased the exposure of
PSI-6130 by approximately 20%. Please see www.clinicaltrials.gov or e-mail
clinicaltrials@pharmasset.com for more information.

"The single ascending doses of R7128 were generally safe and
well-tolerated, and there was no maximum tolerated dose identified in this
study," stated Dr. Michael J. Otto, Pharmasset's Executive Vice President,
Pharmaceutical Research. "The pharmacokinetic profile of the prodrug
indicates good exposure to the active moiety, PSI-6130, and no clinically
significant dose-related adverse events or laboratory abnormalities were
observed. We are pleased with these results and look forward to the continued
development of R7128 for HCV."

Conference Call
    Pharmasset will host a conference call at 8:30AM (ET) on Monday,
September 10, 2007 to discuss the R7128 Phase 1 study results.

    Dial-in Information:
    Domestic callers: +1-800-811-0667 (US/Canada)
    International callers: +1-913-981-4901 (International)

Live audio of the conference call will be simultaneously broadcast over
the internet via a webcast. To access the live webcast, log on to the "Events
& Presentations" section of the Investor Center on Pharmasset's corporate
website at http://investor.pharmasset.com/events.cfm.

Please connect to the company's website at least ten minutes prior to the
start of the presentation to ensure adequate time for a reliable connection
and any software download that may be necessary to listen to the webcast. The
archived replay of the webcast will be available on the Pharmasset website
for two weeks following the conference call.

About Pharmasset

Pharmasset is a clinical-stage pharmaceutical company committed to
discovering, developing and commercializing novel drugs to treat viral
infections. Pharmasset's primary focus is on the development of oral
therapeutics for the treatment of hepatitis B virus (HBV), hepatitis C virus
(HCV) and human immunodeficiency virus (HIV).

Pharmasset is currently developing three product candidates. Clevudine,
for the treatment of chronic HBV infection, is expected to enter Phase 3
clinical trials for registration in the Americas and Europe. Clevudine is
already approved for HBV in South Korea and marketed by Bukwang
Pharmaceuticals under the brand name Levovir. R7128, an oral treatment for
chronic HCV infection, is in a Phase 1 clinical trial through a strategic
collaboration with Roche. Racivir, which is being developed for the treatment
of HIV in combination with other approved HIV drugs, has completed a Phase 2
clinical trial.

About R7128

R7128 is being developed for the treatment of chronic hepatitis C. R7128
is a prodrug of PSI-6130, which demonstrated potency in preclinical studies.
PSI-6130 is a pyrimidine nucleoside analog inhibitor of HCV RNA polymerase,
an enzyme that is necessary for hepatitis C viral replication. Results from
an oral single ascending dose study of PSI-6130 in 24 healthy male volunteers
showed that PSI-6130 was generally well tolerated with no serious adverse
events in doses up to 3000 mg.

R7128 Phase 1 Study Overview

The Phase 1 clinical trial is a multiple center, observer-blinded,
randomized and placebo-controlled study to investigate the pharmacokinetics,
pharmacodynamics, safety, tolerability and food effect of R7128 in healthy
volunteers and in patients chronically infected with HCV genotype 1. This
Phase 1 study is comprised of two parts:

- Part 1 is a single ascending dose study of R7128 conducted in 46
      healthy volunteers. The primary objective of Part 1 is to assess the
      safety, tolerability and pharmacokinetics of R7128 following single
      ascending doses under fasting conditions. The secondary objective of
      Part 1 is to explore the effect of food on the pharmacokinetics of
      R7128. Preliminary data from the single ascending dose portion of the
      study indicate:
        - All doses of R7128 studied were generally safe and well-tolerated.
        - All patients completed the study, and none experienced
          gastrointestinal adverse events or serious adverse events during
          the study.
        - No hematological or laboratory abnormalities of clinical
          significance were noted.

    - Part 2 is a multiple ascending dose study of R7128 conducted in 40
      patients chronically infected with HCV genotype 1 who have 
      previously failed interferon therapy. The primary objective of Part 
      2 is to assess the safety, tolerability and pharmacokinetics of 
      R7128 after once-daily or twice-daily dosing for 14 days. The 
      secondary objective is to assess antiviral activity by measuring 
      the change in HCV RNA.

About Hepatitis C

Hepatitis C is a blood-borne infectious disease of the liver and is a
leading cause of chronic liver disease and liver transplants. The World
Health Organization estimates that nearly 180 million people worldwide, or
approximately 3% of the world's population, are infected with hepatitis C
virus (HCV). The CDC has reported that almost four million people in the
United States have been infected with HCV, of whom 2.7 million are
chronically infected.

Contact
    Alan Roemer, Vice President
    Investor Relations & Corporate Communications
    alan.roemer@pharmasset.com
    Office: +1-609-613-4125

Forward-Looking Statements

Pharmasset "Safe Harbor" Statement under the Private Securities
Litigation Reform Act of 1995: Statements in this press release regarding our
business that are not historical facts are "forward-looking statements" that
involve risks and uncertainties including without limitation, the risk that
there will be a delay in the presentation of safety, tolerability,
pharmacokinetic and food effect data from the R7128 Phase 1 single ascending
dose study, the risk that there will be a delay in the release of R7128
safety, tolerability, pharmacokinetic and antiviral efficacy data from the
R7128 Phase 1 multiple ascending dose study, the risk that the R7128 data
from the Phase 1 R7128 single ascending dose study is not accurate or
representative, the risk that the preliminary data from the R7128 Phase 1
multiple ascending dose study is not accurate or representative, the risk
that our collaboration with Roche will not continue or will not be
successful, the risk that the on-going or anticipated clinical trials for any
one or more of our product candidates will not be successful and the risk
that any one or more of our product candidates will not be successfully
developed and commercialized. For a discussion of these risks and
uncertainties, any of which could cause our actual results to differ from
those contained in the forward-looking statements, see the section of our
Quarterly Report on Form 10-Q for the quarter ended June 30, 2007 filed with
the Securities and Exchange Commission entitled "Risk Factors" and
discussions of potential risks and uncertainties in our subsequent filings
with the Securities and Exchange Commission.

Web site: http://www.pharmasset.com
              http://investor.pharmasset.com/events.cfm