In the present study, we have found that the cell lysate from cultured human normal keratinocytes from foreskin (HFKs) hydrolyzed alpha-N-benzoyl-DL-arginine beta-naphthylamide (BANA), and the BANA hydrolysis occurred most under conditions of 37 degrees C and pH 6.0. This activity was strongly inhibited by leupeptin, which is an inhibitor to cathepsin B. These results suggested that the cell lysate from cultured HFKs contained cathepsin B-like enzyme activity. This is the first report to demonstrate that cathepsin B-like enzyme activity was expressed in the cell lysate from human normal keratinocytes.