Summary: Because captopril alone does not control blood pressure in all patients with essential hypertension, studies were performed to assess the effect of sodium intake and of captopril combined with hydrochlorothiazide, propranolol, and nifedipine. Captopril given for 5 days to normotensive subjects having high, normal, and low sodium intakes reduced blood pressure the most in those on the lowest intake; the fall correlated with that in plasma angiotensin II. When 12 patients with moderate hypertension had hydrochlorothiazide added to captopril their blood pressure fell significantly. When propranolol was added to captopril, however, there was no further fall in blood pressure. When propranolol was added to captopril and a diuretic, pressures measured 4 and 6 h after the last dose of captopril showed reduced values compared with placebo; pressures measured 2 and 12 h after did not. Nifedipine added to captopril reduced blood pressure more than either drug alone. When renin and angiotensin are low, as they may be in essential hypertension, captopril is less effective; its effectiveness should increase if sodium is restricted. Both diuretics and nifedipine increase the effectiveness of captopril; propranolol does not, although it may prolong captopril's action. Experience in patients with resistant hypertension suggests that adding nifedipine to captopril may reduce the need for diuretics, while adding captopril to nifedipine may reduce the need for beta-blockers.