Most of the cardiovascular complications associated with aging are due to adverse-changes in vascular structure and function. The general aim of this research project is to determine whether endothelial function declines with age in physically active populations. The general hypothesis is that endothelial function does not decline with age in physically active populations. To test this hypothesis a cross-sectional model will be used to document the age-related decline in endothelium-dependent vasodilatation in healthy sedentary adults and the lack of such a decline in physically active adults. Endothelium-dependent and -independent vasodilatation will be determined by changes in forearm blood flow (strain-gauge plethysmography) induced by intrabrachial infusions of acetylcholine and sodium nitroprusside, respectively. The nitric oxide synthase inhibitor NG-monomethyl-L-arginine will also be administered intra-arterially to allow the determination of any age-and/or physical activity-related differences in the basal formation and release of nitric oxide. The results of the present study should provide new and clinically useful insight into the influence of habitual physical activity on the age-related decline in endothelial function.