The effect of oxidative stress on endothelial function, platelet function, and fibrinolysis in hypertension with or without glucose intolerance was examined. The endothelium, platelets and fibrinolysis play important roles in the progression of atherosclerosis and interact with each other. We have previously demonstrated that glucose intolerance impairs endothelial function in hypertension, but its precise mechanisms have not been clarified. Hypertensive patients were divided by the results of 75-g oral glucose tolerance test into a normal glucose metabolism group (n = 65) and a glucose intolerance group (n = 47). The plasma level of thiobarbituric acid-reactive substances (TBARS) was assessed as a marker of oxidative stress. Endothelial function was assessed by flow-mediated dilatation (FMD), platelet function by the concentration of ADP dose inducing half-maximal aggregation (EC50), and fibrinolytic parameters by radioimmunoassay. These functions were assessed before and after acute administration of vitamin C. FMD was reduced while TBARS and fibrinolytic parameters were higher in patients with glucose intolerance than in those with a normal glucose metabolism. Vitamin C increased FMD and reduced fibrinolytic parameters significantly in the glucose intolerance group, but not in the group with normal glucose metabolism. On the other hand, the EC50 was similar in both groups. In conclusion, glucose intolerance aggravates oxidative stress, thereby contributing to the impairment of endothelial function in patients with hypertension. These abnormalities affect fibrinolysis but not platelet function.