Complementary DNA-clones for human preproacrosin have been isolated from a human testis cDNA library in lambda gt11. The nucleotide sequence of the 1402 bp cDNA insert includes a 20 bp 5' noncoding region, an open reading frame of 1263 bp corresponding to 421 amino acids (45.9 kdalton), and a 105 bp 3' untranslated region. The deduced amino acid sequence is compared with that recently evaluated from a cDNA clone for boar preproacrosin. The sequence identity is 70%; the leader sequence, the catalytic triad (His, Asp, Ser; which is characteristic for serine proteinases) and the positions of the cysteine residues crosslinking the light and the heavy chain of the active enzyme, acrosin, are conserved in both species. At the C-terminal end, a proline-rich sequence is present in both species; this may represent the species-specificity of acrosin.