SummaryThe activity of angiotensin converting enzyme (ACE) was assessed in human body fluids (serum, seminal plasma, prostatic secretions), in tissue extracts of the testis, epididymis, prostate and skeletal muscle, in split ejaculates and in seminal plasma obtained from patients before and after vasectomy. To ensure the specificity of the results the dependence of ACE activity on specific inhibitors was evaluated. Enzyme activity found in tissues of the male genital tract was considerably higher than that in serum and other tissues. ACE in human seminal plasma is synthesized by the testis, epididymis and prostate in different amounts.