To the editor: We would like to call attention to a potentially dangerous, adverse reaction to epinephrine when combined with propranolol: marked bradycardia and atrioventricular block. These drugs were administered as part of an investigation of the effects of adrenergic agents on cutaneous immediate hypersensitivity. The subject, a 22-year-old man in good health, gave informed consent to a protocol approved by the Committee on Human Experimentation of the University of California School of Medicine, San Francisco. Epinephrine was first administered alone at a rate of 17 µg/min intravenously, and produced a rise in blood pressure (arm cuff) from 110/80 mm