Sodium nitroprusside was used intravenously in patients with malignant hypertension refractory to the standard antihypertensive agents and, in one patient, to diazoxide. The average blood pressure before any antihypertensive therapy was 240/132 mm Hg, and it was essentially unchanged after treatment with methyldopa, hydralazine hydrochloride, furosemide, and reserpine given either singly or in combination. Diastolic blood pressure was reduced to 90 to 100 mm Hg within five minutes of sodium ntiroprusside infusion. Sodium nitroprusside was used continuously for a mean of six days, without marked toxic reactions. Sodium nitroprusside administration was simplified with the use of a constant infusion pump to control infusion rate and by continuous monitoring of the arterial pressure. Gradual substitution of orally given therapy was accomplished by the method presented.