The long-term effect of treatment with captopril was observed in 7 hypertensive patients on maintenance hemodialysis who had been refractory to combined antihypertensive therapy with propranolol and hydralazine. Captopril showed a potent hypotensive effect in all the subjects throughout the study period of 6 months. The blood-pressure reduction during treatment with captopril was associated with a decrease in total peripheral resistance. Cardiac index increased significantly due to a significant increment in heart rate at the 6th month. Plasma renin activity increased significantly at the 3rd month, whereas it decreased at the 6th month. No significant correlation was observed between the blood-pressure response and the pre-treatment level of plasma renin activity.