We hypothesized that abnormal endothelium-dependent vasodilation (EDD) found in older otherwise healthy subjects can be attenuated with long-term endurance training. Ten endurance-trained men, 68.5 ± 2.3 yr old, and 10 healthy sedentary men, 64.7 ± 1.4 yr old, were studied. Aerobic exercise capacity (V̇O(2max)), fasting plasma cholesterol, insulin, and homocysteine concentrations were measured. Master athletes had higher V̇O(2max) (42 ± 2.3 vs. 27 ± 1.4 ml · kg-1 · min-1, P < 0.001), slightly higher total cholesterol (226 ± 8 vs. 199 ± 8 mg/dl, P = 0.05), similar insulin, and higher homocysteine (10.7 ± 1.3 vs. 9.2 ± 1.4 μmol/ml, p = 0.02) concentrations. Brachial arterial diameter, determined with vascular ultrasound, during the hyperemic response was greater in the master athletes than in controls (P = 0.005). Peak vasodilatory response was 109.1 ± 2 vs. 103.6 ± 2% (P < 0.05) in the athletes and controls, respectively. Endothelium-independent vasodilation in response to nitroglycerin was similar between the two groups. The increased arterial diameter during the hyperemic response correlated significantly with the V̇O(2max) in the entire population (r = 0.66, P < 0.002). Our results suggest that long-term endurance exercise training in older men is associated with systemic enhanced EDD, which is even detectable in the conduit arteries of untrained muscle.