The initial study will evaluate the safety and combined antiviral activity of R7227 (ITMN-191), a protease inhibitor, and R7128, a polymerase inhibitor, in 14 days of combination therapy in treatment-naive patients infected with HCV genotype 1.

This direct antiviral combination study represents an important first step in evaluating the therapeutic potential of an all-oral, interferon-free combination treatment for HCV. Roche is uniquely positioned to develop all-oral combination studies in HCV through its collaborations with InterMune and Pharmasset, which provide access to both protease and polymerase inhibitors, respectively.

With InterMune, Roche is developing R7227, an HCV protease inhibitor compound to be used in combination with PEGASYS(R) (peginterferon alfa-2a) and COPEGUS(R) (ribavirin), the current standard of care (SOC). Concurrently with Pharmasset, Roche is developing R7128, an HCV RNA polymerase inhibitor, also for therapy in combination with PEGASYS(R) and COPEGUS(R). Both of these molecules have successfully completed Phase 1 monotherapy studies, have been dosed in combination with PEGASYS(R) and COPEGUS(R) and both have individually demonstrated their efficacy against HCV.

Current standard of care for HCV comprises pegylated interferon plus ribavirin, for a duration that is dependent upon factors such as genotype of the virus. For the most difficult to treat genotype 1 virus, a 48-week treatment course generally results in sustained viral response in about 50% of patients. PEGASYS(R) and COPEGUS(R) are the current foundation of HCV treatment and the preferred pegylated interferon therapy of choice for most HCV antiviral agents in development.

Nick Cammack, Leader of the Virology Disease Biology Leadership Team at Roche stated: "It is exciting to be at the forefront of designing innovative clinical approaches in fighting this chronic disease together with our partners, InterMune and Pharmasset. Our approach demonstrates our strong interest in combining molecules in development and investigating all possibilities that may enable us to deliver a new standard of care for patients with HCV."

Dan Welch, Chairman, Chief Executive Officer and President of InterMune, said, "The goal is to develop a treatment regimen that is better tolerated, shorter in duration and delivers higher sustained viral response rates. We are pleased to participate in the first clinical exploration of an all-oral, direct antiviral regimen towards that goal."

"The combination of oral antiviral therapies for HCV represents an exciting step in the evolution of HCV treatment," stated Patrick Higgins, Executive Vice President of Marketing and Sales at Pharmasset. "We believe the development of an all oral treatment regimen may help attract many more patients into therapy that are currently not on treatment."

About R7128

R7128, being developed for the treatment of chronic HCV infection, is a pro-drug of PSI-6130, a cytidine nucleoside analog inhibitor of HCV RNA polymerase. A pro-drug is a chemically modified form of a molecule designed to enhance the absorption, distribution and metabolic properties of that molecule. R7128 has shown in vitro activity against all of the most common HCV genotypes (1, 2, 3 and 4).

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 enrolling Phase 3 clinical trials for registration in North, Central and South America and Europe. Clevudine is already approved for HBV in South Korea and marketed by Bukwang Pharmaceuticals in South Korea under the brand name Levovir. R7128, an oral treatment for chronic HCV infection, is in a 4-week Phase 1 clinical trial in combination with PEGASYS(R) plus COPEGUS(R). 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 R7227 (ITMN-191)

R7227 is an inhibitor of HCV NS3/4A protease activity, and has produced multi-log10 reductions in circulating HCV RNA in chronic HCV patients when administered for 14 days as monotherapy. In support of clinical studies that will combine R7227 with R7128, including the INFORM-1 study, InterMune, Roche and Pharmasset have investigated in vitro the combined antiviral effect of these compounds.

About InterMune

InterMune is a biotechnology company focused on the research, development and commercialization of innovative therapies in pulmonology and hepatology. InterMune has a pipeline portfolio addressing idiopathic pulmonary fibrosis (IPF) and hepatitis C virus (HCV) infections. The pulmonology portfolio includes the Phase 3 program, CAPACITY, which is evaluating pirfenidone as a possible therapeutic candidate for the treatment of patients with IPF and a research program focused on small molecules for pulmonary disease. The hepatology portfolio includes HCV protease inhibitor ITMN-191 (R7227) in Phase 1b, a second-generation HCV protease inhibitor research program, and a research program evaluating a new target in hepatology. For additional information about InterMune and its R&D pipeline, please visit www.intermune.com

About Roche

Headquartered in Basel, Switzerland, Roche is one of the world's leading research-focused healthcare groups in the fields of pharmaceuticals and diagnostics. As the world's biggest biotech company and an innovator of products and services for the early detection, prevention, diagnosis and treatment of diseases, the Group contributes on a broad range of fronts to improving people's health and quality of life. Roche is the world leader in in-vitro diagnostics and drugs for cancer and transplantation, and is a market leader in virology. It is also active in other major therapeutic areas such as autoimmune diseases, inflammatory and metabolic disorders and diseases of the central nervous system. In 2007 sales by the Pharmaceuticals Division totaled 36.8 billion Swiss francs, and the Diagnostics Division posted sales of 9.3 billion Swiss francs. Roche has R&D agreements and strategic alliances with numerous partners, including majority ownership interests in Genentech and Chugai, and invested over 8 billion Swiss francs in R&D in 2007. Worldwide, the Group employs about 80,000 people. Additional information is available on the Internet at www.roche.com.

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 adverse events could cause the cessation or delay of any of the ongoing or planned clinical trials and/or our development of our product candidates, the risk that the results of previously conducted studies involving our product candidates will not be repeated or observed in ongoing or future studies involving our product candidates, the risk that our collaboration with Roche will not continue or 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 Annual Report on Form 10-K for the fiscal year ended September 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.

Source: Pharmasset, Inc.

CONTACT: Richard E. T. Smith, Ph.D., VP, Investor Relations and Corporate Communications, +1-609-613-4181, richard.smith@pharmasset.com, of Pharmasset, Inc.

Web site: http://www.pharmasset.com/

http://www.roche.com/

http://www.intermune.com/

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