Labetalol is a competitive inhibitor of alpha- and beta-adrenergic receptors and has an antihypertensive action. To determine limb haemodynamic effects, we measured calf blood flow and venous capacitance by venous occlusion plethysmography before and after oral labetalol in 10 patients 3-7 days following coronary bypass surgery. Vascular resistance was calculated as the ratio of mean arterial pressure to arterial flow. The peak effect of labetalol was taken as the point of maximum blood pressure decline, and this interval was selected for evaluation of the limb haemodynamic response. Ninety to 120 min after administration of 100-200 mg of labetalol the mean blood pressure fell from 88 +/- 3 to 79 +/- 3 mm Hg; (P less than 0.005). The mean arterial blood flow registered 5.1 +/- 1.0 ml 100 ml-1 limb tissue min-1 which was not significantly different from the control value of 4.4 +/- 0.8 ml 100 ml-1 limb tissue min-1. The calculated index of limb vascular resistance was not affected by labetalol administration, averaging 37 +/- 12 mm Hg 100-1 ml limb tissue min-1 before labetalol and 30 +/- 11 mm Hg ml-1 100 ml limb tissue min-1 at the time of peak hypotensive effect. There was a slight but statistically significant increment in limb venous volume to 1.9 +/- 0.3 from 1.5 +/- 0.3 ml 100 ml-1 limb tissue (P less than 0.025). Placebo administration produced no consistent changes in blood pressure, arterial blood flow, vascular resistance or venous capacitance.(ABSTRACT TRUNCATED AT 250 WORDS)