44 patients with refractory heart failure (RHF) were treated with a conversion enzyme inhibitor, captopril. Prior to treatment, 26 patients had stage IV RHF and 18 patients had stage III RHF (NYHA). The course of the trial was marked by early deaths (6 months) in 9 cases (20.4%), early treatment failure in 8 cases (18.2%), intolerance in 3 cases (6.8%) and 3 patients (6.8%) were lost to follow-up. 21 patients (48%) were improved by the treatment and were followed for a mean of 16 months +/- 8.6. The mean dosage of captopril was 157 mg per day in 3 oral doses (range: 75 to 300 mg per day). The pulmonary capillary pressure dropped, on average, from 30 +/- 10 mm Hg to 21 +/- 7 mm Hg (p less than 0.01) by the 8th day and remained stable thereafter. The cardiac index increased by 40%. The heart rate decreased by a mean of 10.4%, by the time of the first examination. The mean blood pressure was not significantly modified. Side effects which resolved after changing the dosage were seen in one third of cases: renal failure (4 cases), hypotension (2 cases), hyperkalaemia (1 case). In the long term, 6 patients (2.6%) died after a mean delay of 15.6 +/- 5.3 months.