Highly characterized substrate for herpes simplex virus type 1 protease (HSV-1), which is essential for viral nucleocapsid formation and for viral replication. Enzyme activity was measured using HPLC for the separation of the products from the substrate and for quantitation. The C-terminal cleavage product of HTYLQASEKFKMWG-amide was detected at 280 nm (excitation) and 350 nm (emission) with a fluorescence detector.