The effectiveness of a new beta adrenergic receptor blocking agent, propranolol hydrochloride (Indernal) was explored experimentally by a double-blind study of 20 patients, 16 men and four women, exhibiting classic, essentially stable angina pectoris. Statistical analysis of the results supports the clinical impression of significant benefit in the majority of patients. Reduction in both frequency of anginal pain and nitroglycerin consumption was observed when 160 mg of propranolol was administered daily. Side effects, principally light-headedness, lassitude, muscle aches, and diarrhea, noted by 12 patients were troublesome in 3 patients, but generally lessened with reduction in drug dosage. Conventional laboratory studies performed serially disclosed no toxic effects upon renal, hepatic, or bone marrow systems.