A method of acidic extraction at pH-1.3 was used for quantitative estimation of the proacrosin and acrosin content in boar spermatozoa after various times of storage in four different sperm dilutors. The proacrosin and acrosin contents were correlated with the results of biological tests for sperm penetration in zona-free hamster eggs and sperm survival. The results have shown that proacrosin quantitation should be a convenient biochemical test of sperm fertilizing capacity.