Several parameters of motility and integrity of frozen-thawed spermatozoa are compared with the ability of selected motile, intact spermatozoa to acrosome reaction induced by 0.005% hyamin. Between semen donors there exist distinct individual differences; however only the induced acrosome reaction after heparin treatment showed a significant correlation with fertility. For 12 bulls the nonreturn rates from 334 to 559 services correlated significantly with induced acrosome reaction (r=0.607). The in vitro fertilization of 53 to 93 tubal bovine oocytes with frozen-thawed spermatozoa from five bulls yielded a correlation of r=0.621 with the rate of induced acrosome reaction. The different capacity levels of heparin-treated spermatozoa to undergo acrosome reaction appears to correspond to the varying intensity and kinetics of heparin-mediated head-to-head aggregation of motile cells. The applied functional parameters could be used for the selection of bulls with low fertility in artificial insemination programs, and for spermatozoa donors for in vitro fertilization.