Physical activity can prevent atherosclerotic progression which is characterized by an impaired flow-mediated dilation (FMD) response. Using the postprandial state as a surrogate, some of the mechanisms associated with endothelial dysfunction and physical activity are becoming better understood. Purpose. To determine the endothelium-dependent response (FMD) to a high fat meal (HFM) prior to a bout of moderate exercise and to see if the shear stress stimulus is appropriate for the FMD response. Methods. 9 healthy men [32+/-8 yrs, 80.5+/-21.8 kg, 178.4+/-9.6 cm, 25.3+/-4.9 kg·m-2 (means+/-SD)] completed 4 randomized experimental conditions: (1) Control, (2) Meal only, (3) Exercise only, (4) Meal and Exercise combined. FMD was measured with B-Mode ultrasonography and mean blood velocity with Doppler velocimetry both in the left brachial artery at baseline, 2 hrs, 3hrs, and 4hrs post-baseline measurement. Results. Baseline brachial artery diameter was not different between the 4 experimental conditions. The percent change in FMD2, FMD3, and FMD4 (4.6+/-2.0%, 3.9+/-1.6%, 4.0+/-2.0%, respectively) were significantly lower ( P<0.05) compared to FMD1 (6.4+/-2.0%) in the Meal only condition. When expressed as the percent change from FMD1 in Meal and Exercise, a decrease in endothelial function following the meal (-29+/-26%) was attenuated by the bout of moderate exercise (+22+/-67%, P<0.05). There were no main effects or condition-by-time interactions for shear stress in any of the experimental conditions. Conclusion. These results indicate that the consumption of a high fat meal significantly impairs endothelial function and that a bout of moderate exercise performed after the meal can counteract these negative effects. In addition, it appears that the FMD response is independent of the shear stress stimulus suggesting the presence of another mechanism which impairs endothelial function.