Nicardipine hydrochloride, a dihydropyridine calcium entry-blocking drug, was administered to 66 patients with severe hypertension during three protocols designed to examine the efficacy and safety of this investigation drug. It was shown that nicardipine was uniformly effective in lowering blood pressure to a therapeutic goal of 95 mm Hg. Time to achieve therapeutic effect was dose dependent, and steady-state blood levels were achieved after 8 to 12 hours. Reductions in both systolic and diastolic blood pressure but not changes in heart rate were correlated with plasma concentrations of nicardipine. In dose-ranging studies, the minimal effective dose of nicardipine appeared to be 2 mg/hr; 1 mg/hr was an ineffective dose, and little additional effect was seen above 4 mg/hr. Side effects were modest and consisted of those associated with vasodilation--headache, flushing, and feelings of warmth. In the initial group of patients studied, local thrombophlebitis occurred in a substantial number of patients. This was seen only after 14 hours of infusion. In subsequent studies, the infusion site was changed after 12 hours, and no further cases of thrombophlebitis were seen. Nicardipine appears to be therapeutic agent for parenteral use that shows promise in the treatment of severe hypertension.