AbstractThe involvement of a kallikrein−kinin system in the motility of mammalian spermatozoa has been suggested by several investigators. We found that incorporation of kallikrein (0.1–1.0) unit/ml) in the sperm incubation medium did not enhance the motility of hamster spermatozoa that were already active. However, this enzyme significantly increased the incidence of the acrosome reaction. Trypsin (1.8–18 units/ml) and chymotrypsin (0.34–3.4 units/ml) also increased the incidence of the acrosome reaction, and accelerated its onset. Kinins (bradykinin and kallidin) added to the medium in a wide concentration range (1 ng/ml to 1 mg/ml) had no marked effects on either the motility or the acrosome reaction. A kallikrein−kinin system is apparently not of primary importance at least for the acrosome reaction. The enhancement of the acrosome reaction by exogenous proteinases may be due in part to accelerated removal or alteration of the sperm surface coat (glycoprotein) by the enzyme peior to the acrosome reaction. Exogenous proteinases may also act synergistically with endogenous (acrosomal) proteinases (and other enzymes) in altering membrane proteins and dispersing the acrosome matrix during the course of teh acrosome