The present study was designed to investigate the potential protective effects of melatonin on
potassium dichromate (K2Cr2O7)(hexavalent chromium) induced nephrotoxicity in adult male rabbits. Animals
were randomly divided into four experimental groups. The first group received saline solution daily for 30 days. The second group received melatonin at a dose of 10 mg/kg b.w./day. The third group was treated with 0.4 mg/kg b.w. K2Cr2O7.The fourth groupwas treated with 0.4 mg/kg b.w. K2Cr2O7 plus 10 mg/kg b.w. melatonin. Results showed normal kidney tissue and normal kidney functions in the first two groups. Histopathological observations of the third group showed structural abnormalities in the renal cortex including glomeruli and tubules. Histomorphometric study in the third group revealed significant decreased of the mean values of glomerulus area and glomerulus diameter, while, the mean percentage of the glomerular affection and tubules lumen area showed significant increased. Biochemical results of the third group showed significant increased of the levels of serum urea and creatinine. Melatonin co-treatment to the chromium-administered rabbits attenuated the increase of urea and creatinine and also improved the histopathological and histomorphometrical changes in the kidneys. The present study suggests that melatonin may be useful in ameliorate kidney damage due to chromium toxicity.