Beta adrenergic blockade diminishes the catecholamine-mediated elevations in heart rate and myocardial contractility that characterize postburn hypermetabolism. To examine how these alterations in cardiac performance affect peripheral perfusion, indirect calorimetry and leg blood flow were measured before and then after a 2-hour intravenous propranolol infusion. Five severely burned patients (55% + 7% total burn surface area), given propranolol at 8 micrograms/kg/minute, had a significant reduction in cardiac index and heart rate with an increased leg vascular resistance resulting in a decrease in extremity perfusion. Four healthy volunteers were given propranolol at 5 micrograms/kg/minute, resulting in a comparable decrease in heart rate, yet there was no change in leg vascular resistance or extremity perfusion. In both patient groups, propranolol decreased the plasma lactate concentration. This suggests that in hypermetabolic patients, beta adrenergic blockade reduces peripheral perfusion and that peripheral perfusion is not a principal determinate of plasma lactate levels. Rather adrenergic blockade appears to decrease lactate concentration as a consequence of the inhibition of lipolysis.