The efficacy of labetalol, an alpha and beta receptor antagonist, was evaluated in 12 normotensive patients with stable angina pectoris in a single blind dose ranging study. After a two week period of placebo treatment, labetalol was given in doses of 100, 150, 200, and 300 mg twice daily, each for two weeks. Frequency of angina attacks decreased from 9.4 (SEM 2.3)/week in the control period to 7.3 (2.8), 5.2 (2.6), 3.8 (1.8), and 3.3 (1.9)/week in the four successive treatment periods. In the same periods the number of glyceryl trinitrate tablets consumed decreased from 7.0 (2.6)/week to 5.8 (3.3), 3.9 (2.9), 2.7 (1.8), and 2.6 (2.1)/week. Maximal symptom limited treadmill exercise tests were performed three and 12 hours after dosage at each dose. Exercise tolerance (expressed as seconds of the Bruce protocol) increased from 266 (44) with placebo to 306 (44), 369 (50), 396 (48), and 413 (51) in the four treatment periods. This improvement was accompanied by a significant blunting of the heart rate and blood pressure responses to exercise. Trough point exercise tolerance did not differ significantly from that at three hours after dosage. Thus labetalol is effective as an antianginal agent at doses of 150-300 mg twice daily and is well tolerated by the normotensive patient with angina.