Objectives: To date little is known of the interaction between diabetes and sex hormones in the vasculature. A number of studies suggest that premenopausal diabetic women loose their gender based cardiovascular protection. However, there is insufficient evidence to explain the mechanism underlying the loss of this gender based cardioprotection in premenopausal diabetic women. The objectives of this study were to investigate whether there is a gender difference in the aortic endothelial function in · streptozotocin (STZ, 58 mg/kg, iv)-induced diabetic rats, and the potential role of superoxide and cyclooxygenase (COX) metabolites in diabetes-induced vascular dysfunction.