Celiprolol, 400 mg once daily, and atenolol, 100 mg once daily, were compared in a double-blind placebo-controlled crossover study of 16 patients with stable angina. Both drugs reduced angina frequency and delayed the onset of ischaemia during exercise, although only celiprolol prolonged exercise time. Celiprolol produced less suppression of heart rate than atenolol during exercise, and atenolol, but not celiprolol, lowered resting and exercise cardiac output. Thus, the ancillary properties of celiprolol, including partial beta 2-adrenoceptor agonist activity and direct vasodilating activity, have detectable effects on cardiac function that may be beneficial in patients with angina.