The acrosome reaction was induced by means of low temperature or human follicular fluid (FF) in spermatozoa from 18 patients. Live acrosome-reacted spermatozoa were determined with the triple-stain technique. Both inducers of acrosome reaction had a highly significant correlation with the percentage of acrosome-reacted spermatozoa after induction of the acrosome reaction: (r = 0.9190; P < 0.0001) and the inducibility of AR (r = 0.8472; P < 0.0001). This might indicate that both the non-physiological (low temperature) and the physiological (FF) inducers use the same signal transduction pathway, and demonstrates the usefulness of low temperature induction for diagnostic purposes.