BACKGROUND Celiprolol, a novel beta-blocker, may be more effective than propranolol in unstable angina pectoris because of both its beta 1-receptor selectivity and its vasodilatory property. METHODS Fifty-three patients with angiographic coronary artery disease but uncompromised left ventricular function and with recurrent angina pectoris in spite of bed rest, aspirin, and repeated sublingual administration of nitroglycerin were randomized for 1 week of treatment with equipotent doses of either the nonselective beta-blocker propranolol (80 mg/day) or celiprolol (200 mg/day). RESULTS Angina frequency was higher in the propranolol group (p < 0.01), whereas myocardial oxygen demand as estimated by the double product (systolic blood pressure x heart rate) was equally reduced by the two beta-blockers. Forearm blood flow was higher in the celiprolol group (p < 0.001). A stepwise logistic regression analysis showed that the beneficial effects of the beta-blockers were largely dependent on their effect on peripheral flow, in addition to reduction of the double product. CONCLUSIONS Both celiprolol and propranolol largely reduce angina pectoris frequency in unstable angina pectoris. Celiprolol contributes to nearly complete relief in three times as many patients as propranolol; after adjustment for double product, it did so in eight times as many patients. The similar effects of the two compounds on the double product, and the essentially different effects on peripheral flow, support the theory that celiprolol exerts its beneficial effect to a large extent through its vasodilatory property.