The NS3 protease of hepatitis C virus (HCV) is responsible for the cleavage at the NS3/NS4A, NS4A/NS4B, NS4B/NS5A, and NS5A/NS5B sites of the nonstructural protein. It is essential for viral replication and the formation of infectious viral particles, and thus has been considered as one of the most attractive targets for anti-HCV therapy. Recombinant HCV NS3/4A protease is highly active and can be used with SensoLyte® 490 or 520 HCV Protease Assay Kits (Cat# 71126, 71145) to screen for anti-HCV protease drugs.