Biochemical studies of acrosome reactions in an in vitro hamster sperm capacitation system will be concerned with: (1) The mechanism of the stimulation of acrosome reactions by serum albumin and/or its associated molecules. (2) The identification of endogenous sperm molecules (including enzymes) involved in the acrosome reaction. (3) The interrelationship of exogenous and endogenous molecules in the acrosome reaction.