The effect of verapamil 120 mg t.d.s. was compared with propranolol 160 mg b.d. in the treatment of stable angina pectoris. Nineteen patients were studied in a randomized, double-blind, crossover trial, using patient diaries, exercise-testing and ambulatory electrocardiographic monitoring. Both drugs were given for 1 month. On average the number of attacks of angina was reduced equally by verapamil and propranolol. The degree of electrocardiographic evidence of myocardial ischaemia was decreased by the same amount, but verapamil was significantly more effective in prolonging the exercise time. Both drugs reduced the number of episodes of ST-segment depression during 24 hours of ambulatory electrocardiographic monitoring, which was analyzed in nine patients. It is concluded that verapamil compares very favourably with propranolol in the treatment of stable angina, and is more beneficial in improving exercise capacity.