Twenty patients with moderate (4) to severe (16) hypertension, whose blood pressure (BP) could not be controlled on the previous combined antihypertensive therapy, were investigated. In acute studies the first doses of captopril, 25 and 50 mg led to a significant drop in BP 30 min after administration. The maximum fall in BP was recorded at 90-120 min and this effect was maintained throughout the whole observation period (8 hours). The fall in BP was similar in supine and standing positions and there was no change in the heart rate. During long-term (14.5 months) therapy only 2 out of the 20 patients exhibited continuing good BP control with captopril monotherapy of a maximum daily dose of 150 mg. A comparison of the acute and chronic BP lowering effects of captopril showed that the first dose of captopril caused a significantly greater decrease in BP than chronic monotherapy. However, combined captopril with a diuretic or with a diuretic and calcium antagonist or beta blocker provided a sustained BP control, significantly better than the previously used anti-hypertensive combinations (182 +/- 27/115 +/- 11 mmHg vs 164 +/- 20/104 +/- 11 mmHg p less than 0.05). The Hungarian captopril preparation (Tensiomin), similarly to other captopril products, through its angiotensin converting enzyme inhibition, caused an increase in plasma renin activity and in concentration of plasma angiotensin I and a decrease in plasma angiotensin II. Eight out of the 20 patients developed side effects, which disappeared spontaneously in 4 patients within 2-14 days. Captopril was withdrawn in 3 patients for not achieving satisfactory BP control and/or because of side effects. It is concluded that captopril is safe and effective in the long-term treatment of hypertension, however, majority of the patients with severe forms of hypertension required double or multiple combinations.