The efficacy and tolerability of an infusion of isradipine, a calcium antagonist of the dihydropyridine type, were tested in patients in hypertensive crisis. Ten patients with symptomatic and significant elevations in blood pressure were infused for 12 h with isradipine at 1.2, 2.4, 4.8, and 7.2 micrograms/kg/h (3 h of each infusion level). No untoward effects or adverse reactions were noted. No alterations were observed on electrocardiographic tracings, and blood pressure was significantly reduced only at doses of 7.2 micrograms/kg/h. Thus, isradipine as an infusion is useful and safe for hypertensive crisis, starting at a rate of 7.2 micrograms/kg/h. Higher doses may yet prove to be safe, well tolerated, and even more efficacious.