Eight patients with severe congestive heart failure refractory to conventional therapy, including vasodilators, were given captopril (seven patients) or teprotide (one patient). All had dyspnea, edema, elevated pulmonary wedge pressure (28.0 +/- 2.6 mm Hg), low cardiac index (1.6 +/- 0.1 liters per minute per square meter), and elevated levels of serum creatinine (2.3 +/- 0.2 mg per deciliter [203.3 +/- 17.7 mumol per liter]), blood urea nitrogen (48 +/- 5 mg per deciliter [17.1 +/- 1.8 mmol of urea per liter]), plasma renin activity (21 +/- 7 ng of angiotensin I per milliliter per hour), plasma angiotensin II (271 +/- 51 pg per milliliter), and plasma aldosterone (65 +/- 14 ng per deciliter). After one week of therapy, all indexes improved. Creatinine and p-aminohippurate clearances were also increased (P less than 0.01). Improvement was sustained (more than six months) and was associated with a statistically significant increase in the cardiac ejection fraction (12 +/- 3 to 26 +/- 7 per cent). With a mean follow-up of seven months, the New York Heart Association Functional Class has been reduced from IV to II, and the number of days of hospitalization to less than 10 per cent of that before captopril therapy. We conclude that captopril reduces afterload in advanced congestive heart failure and induces sustained improvements in clinical status and renal function.