RO-9187 is a potent inhibitor of HCV virus replication in the replicon system (IC(50) = 171 +/- 12 nM; CC(50) >1 mM). Pharmacokinetic studies with RO-9187 in rats and dogs showed that plasma concentrations exceeding HCV replicon IC(50) values 8-150-fold could be achieved by low dose (10 mg/kg) oral administration.