ExtractExperimentally induced endotoxemia in the rhesus monkey produced a two- to fourfold increase in plasma triglyceride concentration; glucose administration partially prevented this rise. Plasma free fatty acid and phospholipid values were depressed 40–50% of control values whereas cholesterol values were unchanged. Endotoxin-treated monkeys displayed slowed glucose disappearance (K values, 2.2versus1.1) and higher levels of sugar in blood when given glucose (72 ± 8 mg/100 mlversus151 ± 11 mg/100 ml). These studies indicate that endotoxin has a marked effect on the pattern of substrate utilization by the host.SpeculationAlterations in lipid and carbohydrate metabolism affecting substrate utilization of the host may account for many of the clinicopathologic events associated with endotoxemia. Therapeutic measures designed to increase the availability of metabolic fuels for efficient cellular fuel utilization might be of value to patients during endotoxemia.