Once-daily atenolol and celiprolol were compared in a placebo-controlled crossover study of 16 patients with stable angina pectoris. Atenolol and celiprolol equally and significantly reduced frequency of angina and electrocardiographic evidence of cardiac ischemia. Celiprolol, however, produced less suppression of the double product at 1 mm of ST-segment depression than atenolol, suggesting that actions other than reduction of heart rate may contribute to its antianginal efficacy.