1 The effect of labetalol 100 mg orally twice daily on exercise tolerance has been compared with placebo in 19 normotensive subjects with angiographic evidence of coronary artery disease. 2 Labetalol, at the same work load as during placebo exercise, significantly reduced systolic and diastolic blood pressures, as well as heart rate and rate-pressure product. 3 Similarly, ST segment depression was reduced by labetalol from 2.0 +/- 0.4 to 1.36 +/- 0.6 mm (P less than 0.001), thus enabling an increase in exercise tolerance from a control value of 83.7 +/- 18 to 95.3 +/- 19 W (P less than 0.005). 4 In seven other patients, also with coronary artery disease, the haemodynamic effects of a single 0.6 mg/kg intravenous dose of the drug was evaluated during exercise. 5 Compared with conditions during control exercise, labetalol induced a significant reduction in rate-pressure product from 17228 +/- 2375 to 13445 +/- 2404 mmHg/min (P less than 0.005) and in peripheral vascular resistance from 612.0 +/- 61.2 to 512.7 +/- 36.2 dyn cm-5 m-2 (P less than 0.0025). These events were not accompanied by any change in cardiac index and in dP/dT left ventricular end-diastolic pressure (LVEDP) ratio. 6 These data suggest that labetalol may induce reduction in myocardial oxygen consumption, thereby increasing exercise tolerance in patients with coronary artery disease, without impairment of left ventricular performance.