The effects of cicletanine were compared with those of three other antihypertensive drugs: prazosin, a highly selective alpha 1 antagonist, captopril an angiotensin converting enzyme inhibitor and indapamide a diuretic antihypertensive agent, on young stroke-prone SHR rats with high salt diet; furthermore, vascular reactivity to cicletanine was studied on isolated rat aorta. At an equal dose (30 mg/kg per os) all the drugs prevent the onset of hypertension with the same intensity. The minimal effective dose on blood pressure was 1 mg/kg for both cicletanine and captopril, and 3 mg/kg for indapamide. The action on diuresis and electrolyte excretion occurs at a dose of cicletanine 10 to 30 times higher than that required to produce the anti-hypertensive effect. One of the possible mechanisms of the antihypertensive effects of cicletanine could be due to a direct action of the drug on the vascular wall. This vascular impact could be an interaction with the alpha-adrenoceptor system (apparent pA2 cicletanine = 5.12) or a decrease in the vascular spasmogenic response whatever agonist was studied.