Betaxolol is a new, highly cardioselective, once-a-day beta blocker with a long half-life (mean 16 hours). The antianginal efficacy of 2 doses of betaxolol (20 and 40 mg) given once daily was evaluated and compared with propranolol (40 or 80 mg) 4 times daily. Ninety-two patients completed the 10-week double-blind trial. The resting and exercise heart rate, blood pressure and double product were similar for all treatment arms of the study during placebo treatment. Significant decreases in these measures occurred during active drug treatment when compared with placebo. No significant intergroup differences were noted at rest. Maximal exercise heart rate and double product were significantly lower during treatment with betaxolol 40 mg daily than in the propranolol 40 mg 4 times/day treatment group (p less than 0.05). All patients had chest pain and greater than or equal to 1 mm of ST-segment depression during the baseline placebo exercise test. After 10 weeks of active treatment, 55% of the patients were free of chest pain during maximal exercise (difference not significant between treatments). In the betaxolol 40 mg/day group, fewer (6 of 19; 32%) of the patients developed ST-segment depression with exercise (p less than 0.05) compared with propranolol 80 mg 4 times daily (21 of 26; 81%). Betaxolol appears to be a useful once-a-day cardioselective beta blocker for the therapy of angina pectoris.