The NS3 serine protease enzyme of the hepatitis C virus (HCV) is essential for viral replication.Short peptides mimicking the N-terminal substrate cleavage products of the NS3 protease are knownto act as weak inhibitors of the enzyme and have been used as templates for the design ofpeptidomimetic inhibitors. Automated solid-phase synthesis of a small library of compounds basedon such a peptidomimetic scaffold has led to the identification of potent and highly selectiveinhibitors of the NS3 protease enzyme.