An increased sensitivity of adrenalectomized (Adex) rats to intravenous (IV) injection of recombinant human tumor necrosis factor (rHuTNF) was manifested by a marked increase in the rate of mortality. The rats that died exhibited severe hypoglycemia and hypothermia. Administration of 2.5 or 10 μ g 100 g body weight (3% or 12%) of the lethal dose in sham-operated rats (90 μ g 100 g body weight) rHuTNF caused a mortality rate of 50% or 100%, respectively, within 4 hours of its injection. Pre-administration of dexamethasone or intermittent glucose infusion protected the animals from the lethal effect of rHuTNF. Indomethacin did not change the mortality rate in rHuTNF-treated Adex rats, but prevented it in sham-operated rats. The rats that died exhibited a marked decrease in body temperature, but only Adex rats developed hypoglycemia after low doses of TNF. Pretreatment with dexamethasone prevented the hypothermia in both Adex and sham-operated rats, while indomethacin was effective only in sham-operated rats and did not prevent the hypothermia or the hypoglycemia in Adex rats. In the surviving rHuTNF-treated Adex rats, a rapid increase in body temperature occurred, blood glucose decreased to 30 mg/dL, serum insulin concentration decreased to 6 μU/mL, liver glycogen content was reduced by 98%, and a significant reduction in liver phosphoeonolpyruvate carboxykinase (PEPCK) and liver microsomal glucose-6-phosphatase activities was observed. Repeated administration of glucose IV to rHuTNF-treated Adex rats caused an increase in blood glucose and insulin concentrations, and some repletion in liver glycogen content. Injection of rHuTNF, 2.5 to 10 μ g 100 g body weight, to sham-operated rats caused a significant but slower increase in body temperature. It also induced a 50% and 85% reduction in liver glycogen content, respectively, while reduction in liver PEPCK and microsomal glucose-6-phosphatase activities was observed only after injection of 10 μ g 100 g body weight rHuTNF. Serum glucose and insulin levels remained unchanged even after injection of 40 μ g 100 g body weight, but severe hypoglycemia developed following administration of 90 μ g 100 g body weight rHuTNF. In both Adex and sham-operated rats, rHuTNF injection increased serum triacylglycerol and decreased adipose tissue lipoprotein lipase. It is concluded that adrenalectomy sensitizes rats to the lethal effect of rHuTNF. The increased mortality was associated with severe hypoglycemia resulting from the combined effect of rHuTNF administration and the lack of glucocorticoids on glucose homeostasis, and may be reversed by treatment with either dexamethasone or glucose.