We investigated the effects of melatonin on erythrocyte and renal tissue superoxide dismutase (SOD) and malondialdehyde (MDA) levels in rabbits after the administration of a radiocontrast agent. Twenty-four New Zealand rabbits were divided into four groups, six rabbits in each: control, sham, hydration, and hydration plus melatonin. Rabbits in the control group were sacrificed after the extraction of renal tissue. All other rabbits received a single dose of IV diatrizoat sodium (10 mL/kg). In the hydration group, saline (10 mL/kg IV) was infused at 6 hour intervals. In the hydration plus melatonin group, melatonin (10 mg/kg IV) and saline (10 ml/kg IV) were administered at 6 hour intervals. Venous blood samples were obtained from the rabbits before, and 48 and 72 hours after diatrizoat sodium administration to measure serum urea, creatinine, sodium, potassium, calcium, and erythrocyte MDA levels and SOD activities. Renal tissues were removed at the end of 72 hours, and tissue MDA levels and SOD activities were determined. At 72 hours, erythrocyte MDA concentrations of the hydration plus melatonin animals were significantly lower than those of the sham and hydration groups. However, erythrocyte and renal tissue SOD activities were significantly higher in the hydration plus melatonin group than the other groups. Renal tissue MDA levels of the hydration plus melatonin group were significantly lower than those of the sham and hydration groups. Melatonin has favorable effects on lipid peroxidation and antioxidant status in this animal model of radiocontrast nephropathy.