The endothelial angiotensin I‐converting enzyme (ACE) is organized in two large homologous domains, each bearing a putative active site. However, only one of these sites is probably involved in catalysing the conversion of angiotensin I into angiotensin II. The testicular form of ACE is equally active, encoded by the same gene, but translated from a shorter mRNA. Molecular cloning of the human testicular ACE cDNA indicates that the mRNA codes for 732 residues (vs 1306 in endothelium). The testicular transcript corresponds to the 3′ half of the endothelial transcript and encodes one of the two homologous domains of endothelial ACE, preceded by a short specific sequence. This 5′ specific sequence contains 228 nucleotides and encodes 67 amino acids, including the putative signal peptide followed by a serine/threonine‐enriched region, presumably glycosylated. The testicular transcript corresponds to the ancestral, non‐duplicated form of the ACE gene. Since the carboxyl‐terminal domain of the endothelial ACE is expressed in the testicular enzyme, it is likely that it bears the active site in both forms.