Minoxidil is a potent antihypertensive drug widely used in severe arterial hypertension and in that refractory to treatment. Its effectiveness in less severe forms of hypertension was evaluated in 15 patients who had either a severe to moderate arterial hypertension not previously treated, or who did not tolerate the side effects of other antihypertensive drugs. The usefulness of methyldopa and chlortalidone to prevent a potential minoxidil-induced tachycardia and fluid retention, respectively, was also tested. The patients were initially treated with chlortalidone 100 mg/day, and methyldopa 500 mg/day. Minoxidil was then given in increasing doses until the diastolic blood pressure was equal to or inferior to 90 mmHg. This occurred consistently at doses which ranged from 5 to 50 mg/day (average, 29 mg). Treatment with minoxidil was continued for four months; tolerance to the drugs was not observed. Low doses of methyldopa and chlortalidone were effective in controlling the tachycardia and the retention of sodium and water induced by minoxidil. The three associated drugs were well tolerated and the life quality improved in most patients. Hypertrichosis was the most consistent side effect. Two patients were withdrawn from the study after the blood pressure was controlled by minoxidil, because of the appearance of angor in one, and edema and heart failure in the other.