Acute exercise has consistently been shown to reduce postprandial lipemia, an independent risk factor for atherosclerosis. In a series of three studies, this thesis sought to 1. compare the Influence of acute exercise on postprandial metabolism in normal weight, overweight and obese insulin resistant men 2. determine the influence of acute exercise on endothelial micropartlcles and soluble adhesion molecules, plasma biomarkers of endothellal dysfunction, in the fasted and postprandial states 3. investigate the mechanisms mediating the exercise attenuation of postprandial lipemia, and in particular the role of skeletal muscle lipoprotein lipase (LPL) and the importance of glycogen depletion. In all three studies, recreationally active men (aged 22-45) consumed a high fat mixed meal on the morning following prolonged exercise at 70% V02max, or no exerclse. One study involved two exercise trials, wlth the influence of exercise determined wlth and without post-exercise carbohydrate refeedlng. A 700kcal exercise bout reduced postprandial lipemia similarly (-20%) in normal weight, overweight and obese men, with the magnitude of the attenuation positively related to V02max. Exercise also reduced postprandial insulin though this was unrelated to the reduction in lipemia. Enodthelial microparticles increased postprandially, indicative of endothelial dvsfunction. but this resoonse was not attenuated bv exercise. Soluble adhesion molecules didn't change postprandially or following exercise. The exercise attenuation of lipemia was largely reversed by post-exercise carbohydrate refeeding that repleted muscle glycogen However, LPL activity was not significantly influenced by exercise or by carbohydrate refeeding. Considerable inter-individual variation was evident in the LPL response to exercise, with changes in LPL actlvity inversely related to changes in postprandial lipemia. Taken together, these studies confirm that single bouts of exercise can reduce postprandial Ilpemia, but without enhancing endothelial function. This attenuation is likely to be mediated by changes in muscle LPL activity but also by unknown factors associated with glycogen depletion.