The mammalian zona pellucida is a mixture of glycoproteins, believed to be encoded by three distinct genes, ZP1/ZPB, ZP2/ZPA, and ZP3/ZPC. We have now determined that the true human orthologue of the mouse Zp1 gene is not ZPB, but that there is a distinct human ZP1 gene. Comparison of the human ZP1 and murine Zp1 genes indicates significant conservation of nucleotide and amino acid sequences, of intron-exon size and organisation, and of regulatory sequences. In addition, the mouse and human ZP1 genes are in a region of conserved synteny between human chromosome 11 and mouse chromosome 19.