The metabolism of ethanol (ETOH) is known to increase the cytosolic NADH/NAD ratio and consequently impairs hepatic glucose output in the fasted state. In contrast, one of the characteristic alterations in glucose metabolism produced by the administration of endotoxin is an increase in the de novo synthesis of glucose. Therefore, the present study tests the hypothesis that the acute administration of ETOH will prevent the endotoxin-induced increase in glucose production. In vivo glucose kinetics were determined by the infusion of [6-3H, U-14C]glucose in catheterized conscious rats. The intravenous infusion of tracer glucose, and ETOH (100 mg/100 g b.w./hr) or saline were started at the same time and both continued throughout the experiment. Two hours later the ETOH infusion rate was decreased to maintain the blood ETOH levels between 100 and 160 mg/dl. At 140 min, endotoxin (100 micrograms/100 g b.w.) was injected. ETOH alone did not alter basal values of plasma glucose (5 mM), glucose rate of appearance (Ra; 35 mumols/min/kg) or metabolic clearance (MCR; 7 ml/min/kg). Endotoxin alone increased plasma glucose (80%) and lactate (140%) concentrations, glucose Ra (60%) and recycling (40%) in saline-infused rats, whereas in ETOH-infused animals, plasma glucose and lactate levels were only elevated 40% and glucose Ra and recycling were unchanged. The results show that acute ETOH administration diminishes the increased glucose production and utilization seen in endotoxemia. The attenuation of the endotoxin effect by ethanol is due to inhibition of hepatic glucose production and peripheral glucose utilization.