In a randomized double-blind crossover trial 30 patients with chronic stable angina were studied to compare the antianginal actions of gallopamil (150 mg/day) and nifedipine. With the initial nifedipine dose of 60 mg/day, the trial had to be stopped because of severe exacerbation of angina in 3 patients of the nifedipine group. Twenty-one patients were entered into a second protocol with the nifedipine dose reduced to 30 mg/day. Compared to the preceding placebo period, the exercise time to onset of angina (+ 30%, P less than 0.01) and the total exercise time (+ 18%, P less than 0.01) were prolonged by gallopamil but not by nifedipine (+ 20 and 13%, respectively, not significant) with no significant difference between the test drugs. Four patients became free of angina during exercise testing with gallopamil therapy and one patient with nifedipine. Both agents significantly reduced ST depression at maximal comparable workload by 77% (gallopamil) and 52% (nifedipine) compared with placebo; the difference between the drugs reached borderline significance (P = 0.055). The increase in heart rate and the rate-pressure product at maximal comparable workload was less with gallopamil than with nifedipine (P less than 0.01). In contrast to nifedipine, very few side effects were reported with gallopamil. Thus, gallopamil is an effective antianginal agent whose therapeutic to toxic ratio appears to be superior to that of nifedipine.