The present study was performed in order to compare the efficacy, safety, and tolerability of lisinopril, a long-acting angiotensin-converting enzyme (ACE) inhibitor, with captopril, the shorter acting ACE inhibitor available, in the treatment of elderly patients (mean age 70 +/- 0.5 years) with congestive heart failure (mean left ventricular ejection fraction 33.5 +/- 1%). The study was organized according to a double-blind, parallel-group, randomized multicenter protocol. After a 14-day placebo run-in period, patients were randomized to receive either lisinopril 5 mg orally once per day or captopril 12.5 mg orally once per day. The dose of the study drug could be doubled at 2-week intervals for 6 weeks. The maximal dose was lisinopril 20 mg once per day or captopril 25 mg twice per day. The addition of either captopril or lisinopril to a regimen of diuretics caused a significant increase in exercise tolerance assessed by bicycle ergometry after 12 weeks of treatment (530 +/- 21 seconds vs. 431 +/- 13 seconds, p < 0.01; 555 +/- 19 seconds vs. 463 +/- 12 seconds, p < 0.01, respectively). Both drugs significantly increased left ventricular ejection fraction and stroke volume, were equally effective in improving NYHA class, and were well tolerated, with no differences detectable between treatments. The results of this study indicate that lisinopril 5-20 mg once daily is at least as effective and well tolerated as captopril 12.5-50 mg daily in the treatment of elderly patients with congestive heart failure.