Melatonin ( N-acetyl-5-methoxy-tryptamine )is a neurohormone that is secreted  by a small gland in the center of the brain called the pineal gland. Aging is accompanied by changes in the morphology and physiology of organs and tissues. This process might be due to the accumulation of oxidative damage induced by reactive oxygen (ROS) and reactive nitrogen species (RNS). OBJECTIVES: To assess age –related changes that occur in the lung, liver and kidney of the rat and to investigate the  protective role of exogenous melatonin against these changes. METHOD: Thirty five male albino rats were classified into 3 groups.Group 1 (non aged ) acted as the control group, injected with normal saline intraperitoneal 3 times / week and sacrificed when aged 3 months. Group П remained untreated and sacrificed when aged 18 months. Group Ш was treated with melatonin (1 mg/kg) intraperitoneal 3 times / week and sacrificed when aged 18 months. The antioxidant effect of melatonin was also detected by measuring the level of nitric oxide in all groups. RESULTS: Group П showed marked age-related changes in the examined organs. The lung showed thickening in the wall of the alveoli with increased phagocytic and lymphocytic infiltration. The liver showed vaculation of the cytoplasm and increased phagocytic infiltration .The kidney showed atrophic glomeruli . Most of these changes  were  reduced in group Ш ( treated with melatonin ) except increasing the number of phagocyte especially in the lung . Melatonin also decreased the level of nitric oxide.

 CONCLUSION Melatonin seems to have beneficial effects against age- related changes in the lung, liver and kidney