To establish the role of angiotensin converting enzyme inhibitors in the management of hypertension in the elderly, 16 patients were treated with captopril in a randomized double-blind placebo-controlled cross-over study. Clinic blood pressure, ambulatory blood pressure, renal function and mental performance, with emphasis on mood and psychological well-being, were assessed. Twelve patients, aged 73 (± 4.4) years, completed the study. The doses of captopril used were 50 mg (11 patients) and 25 mg (one patient) twice daily for 4 weeks. Mean (± s.e.m.) clinic sitting blood pressure during captopril therapy was significantly lower than during administration of placebo (172 ± 4.5/83 ± 25 versus 188 ± 4.4/89 ± 3.4mmHg;P< 0.001 /P< 0.05). Mean ambulatory blood pressure was also significantly lower on captopril treatment than during administration of placebo (166 ± 5.3/87 ± 1.6 versus 179 ± 5.1/94 ± 2.4mmHg;P< 0.02/P< 0.02) and this effect was sustained over the dosing interval. Renal blood flow and mental performance were unaltered by treatment. Gastrointestinal discomfort occurred in two patients, one of whom was withdrawn and cough developed in one patient.We conclude that captopril is effective as monotherapy in lowering blood pressure in the elderly.