Thirteen acutely symptomatic malignant hypertensive patients were treated with minoxidil in combination with a beta-adrenergic blocking agent and diuretics or dialysis. The degree of endorgan involvement varied, with the kidney being the most compromised in 11 of 13 patients. In 12 of 13 patients, MABP (mean arterial blood pressure) fell significantly within 72 hours, P less than 0.005. After 20 months of therapy, all have now had a favorable response, with a mean reduction in MABP of 48 mm Hg, and with no adverse cardiac disturbances. In addition, the patients with mild azotemia had an improvement in renal function as determined by a reduction in serum creatinine. PRA (peripheral renin activity) rose with the addition of minoxidil despite therapeutic concentration of serum propranolol and a reduction in MABP and heart rate. It was also noted that those patients who had been on guanethidine prior to minoxidil had a more pronounced lowering of MABP within 72 hours of minoxidil therapy. It is concluded that minoxidil is a safe, fast, and effective agent to achieve rapid and sustained control of MABP in malignant hypertensive states associated with chronic renal insufficiency.