During the process of fertilization, the initial interaction between male and female gametes is mediated by a sperm receptor, designated ZP3, which resides in the extracellular glycoprotein matrix (zona pellucida) surrounding the oocyte. The sperm receptor function of the ZP3 molecule plays a key role in the first step of the fertilization process. Following sperm-oocyte binding, ZP3 triggers the sperm acrosome reaction that releases the protein machinery enabling a spermatozoon to penetrate the zona pellucida. The distribution of these 3 patterns was significantly different between the Caucasian and Japanese populations, as indicated by ZP3-372 allele frequencies of 69 and 21%, respectively. Provided that ZP3-372 mRNA is translated in vivo, differences in the protein gene product might have an impact on human zona pellucida composition.