Z-FA-FMK is an irreversible inhibitor of cysteine proteases, including cathepsins B, L, and S, cruzain, and papain. It also inhibits effector caspases-2, -3, -6, and -7 (IC50 = 6-32 μM) without affecting the initiator caspases-8 and -10. Z-FA-FMK also modulates infection by certain bacteria, parasites, and viruses. It can be used both in cells and in vivo.