The effects of verapamil were assessed in 26 patients with stable exertional angina pectoris in a double-blind, placebo-controlled, randomized crossover protocol using serial treadmill tests. Verapamil, 480 mg/day, reduced anginal frequency from 5.6 +/- 7.3 to 2.2 +/- 3.9 attacks per week (p less than 0.001) and nitroglycerin consumption from 3.4 +/- 4.9 to 1.2 +/- 2.5 tablets per week (p less than 0.05) compared with placebo. Treadmill time increased from 6.4 +/- 2.1 minutes during the placebo phase to 7.5 +/- 1.8 minutes during the verapamil phase (p less than 0.001). Verapamil's beneficial effect appeared to be related, in part, to a 10% reduction of the rate-pressure product at rest (p less than 0.05) and a 12% reduction during submaximal exercise (p less than 0.001). Verapamil also caused less marked ST-segment depressions at peak exercise (p less than 0.05) at a similar rate-pressure product, suggesting a favorable redistribution of coronary blood flow to the ischemic zone. Side effects from verapamil were minimal, consisting mainly of constipation (six patients). Verapamil appears to be a safe and effective drug for treating angina of effort.