In a double-blind, randomized crossover study, the daily administration of 30 to 90 mg of nifedipine lowered blood pressure in a dose-related fashion in 14 patients already taking a beta receptor blocker and diuretic. The duration of the hypotensive response to 20 mg of nifedipine in capsule form, giving as a "step-three" drug to five of these patients, was six to eight hours. A survey of 122 patients with resistant hypertension treated long-term with nifedipine and a control group of 102 similar patients treated with hydralazine revealed that nifedipine at an average dose of 40 mg daily caused a fall in blood pressure similar to that achieved with hydralazine in a dose of 86 mg daily. The side effect profile of both drugs was also similar. Nifedipine may be a useful alternative to existing step-three antihypertensive drugs.