Full length zona pellucida cDNAs from cat, dog and pig that are homologous to the ZP2/rc75 genes from mouse, human and rabbit, a full length zona pellucida cDNA from cat and a gene and full length cDNA from human that are homologous to the rc55/ZP3 alpha genes from rabbit and pig, and full length zona pellucida cDNAs from cat, cow, dog, pig and rabbit that are homologous to the ZP3 genes from mouse, hamster, human and marmoset have been cloned and characterized. The members of these gene families are herein referred to as ZPA, ZPB and ZPC genes to avoid the confusion that currently exists in the zona pellucida of nomenclature. This report is the first to describe the presence all three major zona pellucida genes within individual mammalian species. Within the ZPA, ZPB and ZPC gene families, the DNA and deduced amino acid sequences are highly homologous to each other, and are most homologous between members of the same order within the class mammalia. These results imply that all or most mammalian species express the ZPA, ZPB and ZPC proteins, which form the zona pellucida layer surrounding the oocyte.