Minoxidil (U-10,858) has been shown in several controlled and blind studies and numerous uncontrolled studies to be a potent peripheral vasodilator for use in the management of sustained, severe, accelerating or malignant hypertension and moderate hypertension inadequately controlled by conventional therapy. Some effect may be seen four hours after oral administration with the peak effect being seen between four and 18 hours. The drug has a plasma disappearance half-life of 4.2 hours despite a duration of action of approximately 24 hours, suggestive of extravascular accumulation. Reported dosages range from 2 mg to 80 mg daily, most patients requiring approximately 20 mg daily. Rapid loading schedules have been studied but are not yet widely used. Frequent adverse effects include sodium retention, tachycardia, EKG changes, and hypertrichosis. Pericardial effusion, altered renal function, diabetes mellitus, and changes in plasma renin, urinary norepinephrine, and aldosterone levels have been reported. Other minor problems have been reported infrequently.