Capoten (captopril) treatment was conducted in 39 patients with essential hypertension of stage IIA-IIB and in 4 patients with idiopathic hyperplasia of the adrenals. In 35 patients the hypotensive effect was evaluated following a single administration of captopril in a dose of 12.5, 25 and 50 mg. Twelve patients were treated with this drug alone while in 23 patients it was combined with saluretics. Captopril monotherapy elicited a good and moderate hypotensive effect in 70% of patients with a high and stable hypertension. Both mono- and combined therapy was associated with a decrease in adrenaline and noradrenaline excretion and an increase in uterine kallikrein excretion. The examination of the regional circulation revealed a significant reduction in the resistance and tonus of the arterioles and an enhancement of the blood flow in the forearm as well as an increase in venous tensility. When captopril was combined with diuretics these changes were less marked.