This study was designed to investigate the effects of vitamins C and E combinations on oxidative stress in erythrocytes from streptozotocin-induced diabetic rats. Concentrations of malondialdehyde and reduced glutathione and activities of superoxide dismutase and glutathione peroxidase were compared in 3 groups of 10 rats each (control nondiabetic rats [group I], untreated diabetic rats [group II], and diabetic rats treated with vitamins C and E [group III]). Diabetes developed 3 days after intraperitoneal administration of a single 60 mg/kg dose of streptozotocin in groups II and III. Thereafter, the rats in group III began to receive a combination of vitamins C and E. Six weeks later, the rats in groups II and III had significantly lower body weights and higher blood glucose levels than the rats in group I (all P < .001). Malondialdehyde levels in erythrocytes from group II rats were higher and glutathione, superoxide dismutase, and glutathione peroxidase levels were lower than those from rats in groups I and III (P < .01, P < .01, P < .001, and P < .01, respectively). The treatment with vitamins C and E lowered malondialdehyde levels and increased the antioxidant levels to near control values. The results verify the presence of oxidative stress in diabetes and suggest beneficial effects of vitamins C and E combinations in combating the oxidative stress in this disease. © 2005 Elsevier Inc. All rights reserved.