['To examine involvement of oxidative stress in the pathogenesis and vascular complications of diabetes.', 'This cross sectional study was conducted at the Joint Laboratory Office (JLO), Dokkyo Medical University Koshigaya Hospital, Koshigaya, Japan from April 2010 to December 2011. Fasting glucose, glycosylated hemoglobin (HbA1c), serum lipids, urinary albumin excretion (UAE), ankle brachial index and pulse wave velocity were measured in 51 patients with type 2 diabetes and 20 healthy controls. The fundus oculi and Achilles` tendon reflex were also examined in the patients. Oxidative stress was measured by a reactive oxygen metabolites (ROM) test and antioxidant potency was evaluated by a biological antioxidant potential (BAP) test in the Free Radical Analytical System (FRAS)-4. Superoxide dismutase (SOD) activity was assayed using electron spin resonance (ESR).', 'Diabetic patients tended to have increased ROM compared with healthy subjects, and ROM showed a marked increase with progression of diabetic retinopathy. A significant reduction of BAP was found in patients who were smokers, and BAP was significantly negatively correlated with UAE (p=0.029). Serum SOD activity significantly decreased with progression of diabetic retinopathy (p=0.017).'] Are oxidative stress and antioxidative potency closely associated with diabetic retinopathy and nephropathy in patients with type 2 diabetes?