Isradipine (Sandoz PN 200-110), a new dihydropyridine calcium channel antagonist, was evaluated in a randomized, double-blind, placebo-controlled trial for antihypertensive efficacy in 24 patients with essential hypertension. Two groups were studied: one received placebo throughout the entire study (n = 12) and the other received isradipine (n = 12), 2.5 mg b.i.d., for the first week, 5 mg b.i.d. the second week, and 10 mg b.i.d. the third week after an initial 3-week baseline placebo period. Blood pressure was measured approximately 3 hours after dosing. Isradipine, at a total daily dose of 10 mg, lowered average supine diastolic blood pressure 11.8 mm Hg, with only a 3.5 mm Hg decrease in systolic blood pressure compared with baseline. At a total daily dose of 20 mg, average supine diastolic blood pressure decreased 14.8 mm Hg and supine systolic blood pressure declined 13.9 mm Hg; both were significantly decreased compared with placebo or baseline. Heart rate was increased only minimally by isradipine. Renin level activity was increased slightly by isradipine. No serious adverse clinical or laboratory experiences were noted. Isradipine appears to be effective in lowering blood pressure without reflex tachycardia.