In the present study we have cloned and sequenced two testis-specific cDNAs 0.3 .3 kb and 1.6 kb) encoding a human sperm protein, designated HSpl7. Each cDNA gave rise to identical protein sequences and differed only in the 5′ untranslated region. The predicted amino-acid sequence revealed a protein of 17.5 kDa which exhibited a high degree of homology with both rabbit and mouse SpIT Analysis of native and recombinant Sp 17 by SDS-PAGE has shown the apparent molecular weight of the protein to be 24.5 kDa.