Ninety-one doses of diazoxide were administered intravenously to 41 patients with hypertensive crises. Diastolic blood pressure was reduced from an average of 139 to 98 mm Hg within 10 minutes. On the basis of a retrospective analysis of the response of diastolic blood pressure, it was possible to determine within 10 minutes of injection whether a second dose would be required. Therapy was judged to be effective in 38 of 41 patients; 35 percent of injections were ineffective. Concomitant administration of furosemide was not shown to have a beneficial antihypertensive effect. Mean blood urea nitrogen was 59.5 mg/100 ml initially and was not significantly different 2 weeks after therapy. None of the patients demonstrated clinical evidence of diazoxide-induced deterioration of coronary circulation. Electrocardiograms obtained 2 weeks after diazoxide therapy failed to show evidence of new ischemic changes. Only 9 percent of patients complained of side effects, and these were transient and relatively innocuous. It is concluded that diazoxide is both safe and efficacious in the management of hypertensive crises.