The efficacy of verapamil (360 mg daily) in the treatment of patients with chronic stable angina pectoris was compared with placebo. 28 patients were studied in a placebo-controlled double-blind crossover trial of 2 weeks each and afterwards on long-term verapamil. Exercise tests were performed at the end f the placebo period, and after 2 weeks and 4 weeks on verapamil. On placebo, angina developed in all 28 patients during treadmill tests; the mean exercise time was 6.6 min (SEM +/- 0.5 min). The mean exercise time increased to 9.2 (+/- 0.8) min at 2 weeks, and 11.2 (+/- 0.8) min at 4 weeks on verapamil. In 15 and 20 patients out of the 28 angina did not develop during treadmill exercise at 2 and 4 weeks respectively. Trinitrin consumption also decreased. There was a significant improvement in ST-segment changes. Constipation (in 7 patients) and reversible PR-interval prolongation (in 2 patients) were the only side effects. No patient had clinical signs of heart-failure. Thus verapamil (360 mg daily) may be useful in the management of chronic stable angina.