Since the end of 1976 ten orally active converting enzyme inhibitors [SQ 14,225 (captopril), MK 421 (enalapril), MK 422, MK 521 (lysinopril), RHC 3659, CGS 13945, CGS 13928C, CGS 14824A, Hoe 498, S 9490-3, and Ro 31-2848] have been evaluated by our group in normal volunteers. Their ability to blunt the pressor response to exogenous angiotensin I and their effect on the different components of the renin-angiotensin system were tested. This approach has made it possible to establish the efficacy of the different molecules and to predict with a considerable degree of accuracy onset and duration of action of the various compounds as well as the doses needed to treat hypertensive patients. All ten molecules were effective in blocking converting enzyme and thereby the pressor response to angiotensin I. Potency and time course of the inhibition varied considerably among the compounds. Thus, a number of highly effective angiotensin-converting enzyme inhibitors are actually in clinical evaluation and several of them should become available for general clinical use within a few years.