SummaryThe antihypertensive effect of an orally angiotensin-converting enzyme inhibitor, captopril (SQ 14225), alone or associated with hydrochlorothiazide has been assessed in 22 moderate to severe hypertensive patients (20 essential, 2 renovascular) for periods ranging from 1 to 14 months. Blood pressure decreased markedly in all patients with large individual variability. The mean supine diastolic blood pressure fell by 18 % after one month of treatment with captopril alone (mean dosage: 230 mg/day, range 50–450). The main fall in blood pressure occurred at 25 mg t.i.d. Increasing the dose of captopril from 25 to 100 mg t.i.d. did not enhance the magnitude of the anti-hypertensive effect. The addition of hydrochlorothiazide produced a further hypotensive effect in four out of six patients. Captopril alone or combined with hydrochlorothiazide achieved satisfactory control of the blood pressure in 13 out of 14 patients at the 34th week including 7 patients previously resistant to conventional tritherapy.No relationship between the fall of blood pressure and the pretreatment levels of plasma renin activity (n = 18, r = 0.33) was observed.There was no evidence of orthostatic hypotension.Adverse effects included diffuse joint pain, transient rash and taste disturbance necessitating reduction or interruption of captopril in two patients.Ada Cliii llelg 36, 6, 286–93