We cloned a human protein (Hzyg) homologue to Caenorhabditis elegans Zyg-11, an essential protein for cell division at the initial developmental stages of this species, and to a Drosophila melanogaster gene product (Mei-1) which is likely to be involved in meiosis. Hzyg mRNA encodes a protein of 766 amino acids (88 kDa), 14% of which are leucine residues, with some being arranged in four leucine rich repeat motives usually involved in protein-protein interactions. Hzyg is encoded by a single gene, located on chromosome 9q32-q34.1, and transcribed as two mRNA: a 5 kb transcript strongly expressed in testis and skeletal muscle and barely detectable in other human tissues, and an abundant 3.1 kb mRNA detected only in the testis. By using in-situ hybridization and immunohistochemistry, we clearly established the presence of Hzyg expression in pachytene spermatocytes (stage V) and spermatids (stage I and/or II) around the time of meiosis. The cell specific expression of Hzyg transcripts in testis, and the conservation of this gene among distant species, suggest that this protein may have an important role during meiosis.