Objective: Endothelium-dependent vasodilatation (EDV) could be impaired in patients with diabetes mellitus or hypercholesterolemia. It has been reported to be improved by treatment with antioxidants or antihyperlipidemic drugs. An oral antidiabetic agent troglitazone possesses antioxidative action as well as effects to improve insulin sensitivity. In this study, we examined the effect of troglitazone on impaired EDV in non-insulin-dependent diabetes mellitus (NIDDM).