The effect of propranolol hydrochloride therapy for angina pectoris was evaluated by double-blind trial in 121 patients with the anginal syndrome. Ninety-five patients had coronary artery disease, and 26 had normal coronary arteries. Successful therapy was achieved in 83 patients (86%) with coronary artery disease, whereas only six (23%) with normal coronary arteries responded favorably. Not distinguishing features could be found between those patients with coronary artery disease successfully treated with propranolol and those who failed to respond. Side effects occurred in 31% of the patients but necessitated withdrawal of treatment in only two instances. These results indicate that propranolol is highly effective in the prolonged treatment of angina pectoris when this is caused by coronary atherosclerosis and the dose of drug is individualized for each patient.