Diclofurime is a non-inotropic arterial vasodilator and an antagonist to calcium transport. We studied its antihypertensive effect in 16 hypertensive subjects. When given alone at an average dose of 240 mg/day, it induced an overall significant diminution of systolic and diastolic arterial pressure. Among the 16 subjects studied, diclofurime lowered arterial pressure below 150/90 mm Hg in seven, induced an improvement in arterial pressure in six, and showed no effect in three. When hypertension is not controlled with 450 mg diclofurime in 3 doses/day, it may be given in association with acebutolol. Diclofurime is well tolerated. The most troublesome side effects noted were headache, cardiac erethism, asthenia and edema in the lower limbs. These clinical signs were usually transient. Among these 32 patients side effects required interruption of treatment in three. Laboratory follow-up was made on day 78 and 180 after initiation of treatment. No significant change in results was noted. Renal function was studied in seven patients having normal renal function and in six chronic renal failure patients whose inulin clearance was about 30 ml min-I. It was observed that in the normal subject, the injection of a loading dose of 40 mg diclofurime followed by a maintenance dose of 80 mg during one hour induced a slight increase in glomerular filtration and a greater increase in renal blood flow; the filtered fraction was thus diminished. Diclofurime induced a clear and sustained increase in excretion of water and sodium chloride without modifying urinary excretion of potassium. In severe renal failure, no significant changes in glomerular filtration, renal blood flow or electrolyte excretion were observed with diclofurime.