The effect of propranolol hydrochloride in the long-term treatment of angina pectoris was evaluated in 65 patients with severe ischemic (coronary artery) heart disease; 57 were followed up for 6 to 24 months and of these, 37 exhibited a sustained 50% reduction in the frequency of anginal pains and 36 of 54 had a 50% reduction in nitroglycerin requirements. Each patient had a dose threshold (between 160 to 400 mg per day) at which maximum relief was attained. Eight of 65 patients died of myocardial infarction or suddenly; 6 had congestive heart failure; 2, asthma; and 3, severe gastrointestinal symptoms. The results indicate a long-term beneficial effect of propranolol in angina pectoris for periods up to two years. Despite significant symptomatic improvement, a mortality of 12.3% suggests that propranolol does not alter the natural history of severe coronary artery disease.