The functional significance will be investigated of physiological and biochemical changes taking place during acquisition of fertilizing ability by spermatozoa. These processes will be studied using new methodology made possible in part by discoveries in our laboratory. The functional relationship between the acrosome reaction and sperm penetration of the egg investments (granulosa cell layer and zona pellucida) will be investigated using a micro-incubation in vitro fertilization system that we have devised, featuring chemically defined factors that sustain sperm motility. This system will permit the fertilizing sperm to be identified and details of its acrosomal condition to be recorded as it traverses the egg investments. Information will also be provided on the location within the egg-cumulus complex of the putatuve acrosome-reaction inducing factor. This information could eventually assist elucidation of the mechanism of the acrosome reaction, which is presently unknown. Related studies will be performed to examine biochemical parameters of sperm capacitation/acrosome reactions (cyclic nucleotide and phospholipid changes, and pharmacological parameters) using a new technique that permits comparative data to be obtained on highly motile but non-capacitated sperm. This study will focus critically on biochemical properties of sperm and events that are directly concerned in the capacitation/acrosome reaction sequence. The overall study will provide new, precise data on processes taking place in sperm that lead to fertilization; at present these mechanisms are obscure. Such information is urgently needed in order to facilitate productive research on the alteration of human fertility characteristics.