We studied the variations caused by stress in LPL activity, LPL-mRNA and local blood flow in LPL-rich tissues in the rat. Stress was produced by body immobilization (IMMO): the rat's limbs were taped to metal mounts, and its head was placed in a plastic tube. Chronic stress (2 hours daily of IMMO) decreased total LPL activity in mesenteric and epididymal white adipose tissue (WAT), and was accompanied by a weight reduction of these tissues. In limb muscle, heart and adrenals, total LPL activity and mRNA levels increased, and in plasma LPL activity and mass also increased. Acute stress (30 minutes IMMO) caused a decrease in total LPL activity only in retroperitoneal WAT and an increase in pre-heparin plasma active LPL; but the overall weight of this tissue did not vary significantly. We propose an early release of the enzyme from this tissue into the blood stream by some unknown extra-cellular pathways or other local mechanisms. These changes in this key energy-regulating enzyme are probably induced by catecholamines. They modify the flow of energy substrates between tissues, switching the WAT from importer to exporter of free fatty acids and favoring the uptake by muscle of circulating triacylglycerides for energy supply. Moreover, we found that acute stress almost doubled blood flow in all WAT studied, favoring the export of free fatty acids.