Heart failure is a common cardiovascular disorder that increases in prevalence with age. Older patients may respond differently than younger patients to the various classes of drugs used in the treatment of congestive heart failure (CHF). The responses of older patients (at least 65 years of age) were evaluated as part of a large multicenter trial utilizing angiotensin-converting enzyme (ACE) inhibitors in the treatment of CHF. A prospectively planned subgroup analysis of older CHF patients' therapeutic response to the long-acting (approximately 24-hour) ACE inhibitor lisinopril was compared with their response to captopril, a short-acting (less than eight-hour) ACE inhibitor. Symptomatic improvement occurred in both the lisinopril and captopril groups. Exercise duration also improved for patients treated with both agents. However, there was a tendency for lisinopril to be more effective than captopril (p = 0.08). Thus, the low level of renin activity often found in the plasma of older patients did not decrease the ability of the ACE inhibitors to improve effort tolerance. Left ventricular ejection fraction increased in patients treated with lisinopril but not in those treated with captopril. The improvement in left ventricular ejection fraction with lisinopril may be indicative of a more favorable prognosis in patients with CHF, since another long-acting ACE inhibitor, enalapril, reduces the rate of mortality associated with CHF. ACE inhibitors were generally well-tolerated by the older patients in the study. Therefore, ACE inhibitors appear to offer a useful therapeutic approach to the management of CHF in the older age group.