The primary purpose of the present study was to correlate the activity of the sympathoadrenal system with the hemodynamic response of the primate kidney to endotoxin. Sooty Mangabey and Rhesus monkeys were anesthetized, and the left kidney of each animal was exposed through a retroperitoneal approach. Renal venous blood was drained into a reservoir for blood flow measurement. Plasma catecholamines were determined by a fluorometric trihydroxyindole procedure. Monkeys not given endotoxin showed relatively constant renal hemodynamic parameters for two hours. In monkeys administered endotoxin, mean renal artery pressure decreased from 118 to 49 mm Hg, blood flow fell from 4.6 to 1.6ml/min/g, and renal vascular resistance significantly increased. Renal denervation reduced renal vasoconstriction after endotoxin. Plasma catecholamine levels were not higher than those of the controls. Our data suggest that renal vasoconstriction is not due to circulating catecholamines, but occurs mainly as a result of sympathetic stimulation. Autoregulation was not present prior to endotoxin, and renal pressure-flow relationships were unaltered during the post-endotoxin period.