Endothelial function is known to be impaired in chronic smokers possibly by oxygen-derived free radicals. Dietary supplement of antioxidant vitamins may provide protection against endothelial dysfunction. To investigate whether chronic combined administration of vitamin C and E can improve endothelial function, we measured flow-mediated vasodilation (FMD, endothelium-dependent vasodilation) and sublingual glyceryl trinitrate induced vasodilation (0.3 mg, GTN-D, endothelium independent vasodilation) in the brachial artery in 11 young chronic smokers aged 25 +/- 3 years by high resolution ultrasound. FMD was measured as percent diameter changes from baseline to hyperemic conditions (1 min after 5 min occlusion of forearm artery). Each subjects had neither the other coronary risk factors nor organic disease. FMD and GTN-D were examined 3 times in each subject; at baseline, at the end of 4 weeks oral administration of vitamin C (1 g/day) and vitamin E (500 mg/day) and at 4 weeks after cessation of vitamins. FMD was significantly increased from baseline in the treatment phase of vitamins and returned to baseline levels after the cessation. Vitamins had no effect on GTN-D. In conclusion, chronic combined dietary supplement of vitamin C and E improves endothelial function and might have preventive effect against the progression of atherosclerosis in smokers. However, this beneficial effect was reversed after cessation.