PURPOSE: Exercise training has numerous health benefits, and in patients with type 2 diabetes mellitus and metabolic syndrome, it can improve insulin sensitivity and glucose control. A recent publication suggests that antioxidant vitamins (C and E) block these effects on blood glucose. This investigation was undertaken to determine whether antioxidant vitamins ameliorate the beneficial effects of cardiac rehabilitation and exercise training (CRET) on insulin sensitivity and glucose metabolism in patients with coronary heart disease (CHD).; METHODS: We assessed CHD risk factors, including clinical indices of glucose metabolism, and evaluated the effects of exercise training in 315 patients with CHD with diabetes mellitus and/or metabolic syndrome before and after a 3-month program of CRET. Patients were divided into 2 groups based on self-reported antioxidant vitamin (vitamins C and E) consumption.; RESULTS: Both groups, 113 patients (36%) consuming vitamins (Vits group) and 202 patients (64%) who reported no vitamin use (no-Vits group) were statistically similar at baseline. Following CRET, patients improved exercise capacity (+10%, P < .0001), fasting blood glucose (-7%, P < .0001), percent body fat (-3%, P < .0001), high-sensitive Creactive protein (-31%, P = .003), and various lipids and behavioral parameters, but there was no significant improvement in glycosylated hemoglobin following formal CRET. Both Vits group and no-Vits group achieved statistically similar improvements in fasting blood glucose, body fat, and other CHD risk factors.; CONCLUSIONS: Commercially available antioxidant supplements (mean dose of 400 IU of vitamin E and 500 mg of vitamin C) do not ameliorate the health benefits of exercise training, including fasting blood glucose, in CHD patients with manifest diabetes mellitus and/or metabolic syndrome.