In the present study, leukocyte lipid peroxidation, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and serum and leukocyte vitamin C levels of patients with type II diabetes mellitus and healthy controls were investigated. Patients consisted of 53 cases (23 male, 30 female) aged 35-75 years and controls of 34 subjects (15 male, 19 female) aged 34-66 years. Leukocyte lipid peroxidation of diabetics was significantly increased (P < 0.05) whereas vitamin C level was decreased (P < 0.05) compared to those of controls. There was no significant difference in the other parameters. Also, there was no correlation between the above parameters and HbA1c and glucose levels. Our results show that leukocytes of diabetics are affected by oxidative stress which might be a reason for decreased microbicidal activity.