With orally active angiotensin converting inhibitors it is now possible to block the renin-angiotensin system chronically. These agents given alone normalize blood pressure of many hypertensive patients. In the remaining, an additional salt subtraction, induced for example by diuretics, is necessary to further reduce blood pressure. In patients with congestive heart failure, angiotensin converting enzyme inhibitors increase cardiac output and exercise capacity, both acutely and chronically. Adverse reactions resulting from blockade of the renin-angiotensin system can be predicted to a large extent and therefore are most often easily avoided. Angiotensin converting enzyme inhibitors like captopril and enalapril, because of their efficacy and good acceptability are likely to become important drugs for the treatment of hypertension and congestive heart failure.