SummaryAngiotensin-I-converting enzyme is responsible for the conversion of angiotensin I to the potent vasopressor angiotensin II and for degrading the vasodepressor bradykinin. Several converting-enzyme inhibitors have been synthesized of which captopril has been most widely used in human hypertension. This review deals with its pharmacology, haemodynamic effects, mechanisms of action, clinical usefulness and side-effects. It is concluded that converting-enzyme inhibitors are a new and interesting group of antihypertensive agents. However, the toxicity of the first molecule, captopril, remains a serious problem: prescription of this drug should be limited to specific forms of hypertension.