Seventeen patients who were partially or totally refractory to maximal doses of conventional antihypertensive agents were treated with minoxidil. Three patients were receiving long-term maintenance dialysis. Propranolol and diuretics were given to prevent reflex tachycardia and fluid retention. Initial control of blood pressure was excellent in 16 patient. In one patient, diastolic blood pressure remained unchanged (120 mm Hg) despite 60 mg of minoxidil and volume depletion. In three other patients, secondary resistance developed, and the addition of guanethidine was necessary. The main side-effects were fluid retention (in eight) and hypertrichosis (in ten), accompanied in some by a peculiar coarsening of the facial features. Renal function stabilized or improved in most, and urine output increased in the three hemodialysis patients. We conclude that minoxidil is a valuable drug in severe hypertension.