The intravenous administration of bacterial endotoxin to fasted rats elicited basal portal and systemic venous hyperinsulinemia and hyperglucagonemia. Enhanced pancreatic secretion of insulin and glucagon was implied by the elevated portal venous hormonal levels. Elevated insulin and glucagon levels were present at 4 hr after a 33 m̈g/100 gm intravenous endotoxin dose despite no fluctuation of the plasma glucose concentration. The role of the liver in the pancreatic hormonal response to endotoxin was investigated by infusing lipopolysaccharide slowly into the portal vein or systemic inferior vena cava. At doses of 33 and 100 m̈g per 100 gm, endotoxin administered via the systemic route stimulated significantly greater insulin and glucagon responses than did portal administration. Furthermore, rats with acute liver injury induced by partial (67%) hepatectomy, which depressed Kupffer cell phagocytosis, did respond to the 33 m̈g per 100 gm intraportal endotoxin dose with significantly greater hyperinsulinemia and hyperglucagonemia. These data suggest that hepatic Kupffer cells normally function to remove lipopolysaccharideo from the portal venous blood and that at least at low pharmacological doses the pancreatic hormonal response to endotoxin is mediated by an unknown systemic mechanism.