Pharmasset is a clinical-stage pharmaceutical company focused on discovering, developing, and commercializing drugs to treat viral infections. Co.'s primary focus is on the development of nucleoside/tide analogs as oral therapeutics for the treatment of chronic hepatitis C virus (HCV) infection. Co. has three clinical-stage product candidates advancing in clinical trials in various HCV populations as follows: Co.'s pyrimidine, PSI-7977, an unpartnered uracil nucleotide analog polymerase inhibitor; Co.'s purine, PSI-938, an unpartnered guanine nucleotide analog polymerase inhibitor; and mericitabine (or RG7128), a nucleoside analog polymerase inhibitor.