Comparison of sublingual captopril and nifedipine in immediate treatment of hypertensive emergencies. A randomized, single-blind clinical trial. Sublingual captopril (25 mg) was compared with sublingual nifedipine (10 mg) to determine their effectiveness and safety in the treatment of hypertensive emergencies. In nine of 10 patients who received sublingual captopril, mean (+/- SD) systolic blood pressure and diastolic blood pressure dropped from 245 +/- 39 to 190 +/- 25 mm Hg (P less than .0025) and from 144 +/- 8 to 115 +/- 8 mm Hg (P less than .001) at 50 minutes, respectively. The hypotensive effect of the drug was maintained for a mean of 4 hours. In six of nine responders to sublingual captopril, blood pressure-lowering effect was associated with a clear improvement of end-organ failure within 60 minutes. There were no side effects, including a dangerous fall in blood pressure or reflex tachycardia. Sublingual nifedipine lowered diastolic blood pressure and systolic blood pressure in eight of 10 patients. The hypotensive effect of nifedipine was more rapid than that of captopril (10 vs 20 minutes for diastolic blood pressure and 20 vs 30 minutes for systolic blood pressure, respectively), but no difference was observed in the time or in the magnitude of peak hypotensive effect between the two treatments, nor was a difference observed in the duration of hypotensive effect. In six of eight responders to nifedipine therapy, a clear improvement of symptoms and signs of end-organ failure was observed within 60 minutes. In three patients, minor side effects were observed. We conclude that sublingual captopril effectively and safely lowers arterial blood pressure in patients with hypertensive emergencies. 