In sepsis and endotoxemia, metabolism is characterized by accelerated catabolism. In the present study, lipolytic responsiveness of subcutaneous and mesenteric adipose tissue to the sub-lethal dose of endotoxin injection (5 mg/kg) was evaluated using microdialysis techniques in rats. All rats were urethane-anesthetized and implanted with microdialysis probes in their subcutaneous and mesenteric adipose tissue. Lipolysis in each adipose tissue was assessed by measuring the glycerol concentration (an index of lipolysis) in the dialysate from the microdialysis probe. Lipolysis was continuously monitored for 7-hours, prior to and following the injection of endotoxin. The control animals were injected with only saline. Lipolysis in subcutaneous adipose tissue began to increase by 1-hours after endotoxin injection, and reached a peak 60% higher than the basal level by 2-hours after injection. This activated lipolysis after endotoxin was markedly greater than that in the control animals and maintained for 5 hours. In mesenteric adipose tissue, lipolysis after endotoxin injection was greater than in the control animals, but not significant. The endotoxin-induced lipolysis in the subcutaneous adipose tissue was significantly greater than that in the mesenteric adipose tissue. We conclude that the sub-lethal dose of endotoxin injection cause active lipolysis in adipose tissues, and that the lipolytic responsiveness to endotoxin in subcutaneous adipose tissue is greater than in mesenteric adipose tissue.