The aims of this study were to observe the changes in antioxidative defense enzymes and renal morphology after 7,12-dimethyl-benz[a]anthracene (7,12-DMBA) administration in mice and to investigate the possible protective effects of melatonin against 7,12-DMBA-induced renal damage in comparison with vitamin E + selenium (vit E + Se). Forty female mice were divided into four groups: control, DMBA, DMBA + vit E + Se and DMBA + melatonin. In the DMBA group, mice were given injections of 7,12-DMBA (20 mg/kg). DMBA + vit E + Se group mice received injections of 7,12-DMBA + vit E + Se (20 mg/kg + 90 mg/kg + 1.8 mu g/kg). In the melatonin group, mice were given injections of 7,12-DMBA + melatonin (20 mg/kg + 4.2 mg/kg). The experiment lasted for 21 days. Mice were killed and the kidneys were taken for enzyme analyses and histologic examination. Catalase (CAT) and glutathione peroxidase (GSH-Px) activities were found significantly decreased in the DMBA group and in the DMBA + vit E + Se group when compared with the control group (P < 0.05), whereas CAT and GSH-Px activities were found significantly elevated in the DMBA + melatonin group when compared with the control (P < 0.05) and the DMBA group (P < 0.01). Exposure to DMBA resulted in tubular alterations in renal cortex. Morphometric analysis revealed proximal and distal tubular damage (P < 0.05). These alterations were found to be prevented by melatonin but not with vit E + Se administration. These results reveal that melatonin stimulates CAT and GSH-Px activities and prevents renal injury better than vit E + Se combination in mice kidneys.