C. kistolyticum collagenase has been shown to be inhibited by acetylsalicylic acid, flufenamic acid, and indomethacin. Effects with phenylbutazone were variably manifested as inhibition or activation depending upon the concentration of drug used. Cortisone acetate induced activation of collagenase while slight inhibition was found with dexamethasone. Crystalline pancreatic elastase (porcine) was shown to be inhibited by phenylbutazone but cortisone acetate and dexamethasone had no effect. Flufenamic acid, acetylsalicylic acid, indomethacin, and some structurally related compounds caused activation of the enzyme.