To investigate the role of melatonin in D-galactose-induced amnesic mice, the avoidance/escape and water maze tests were performed to evaluate their learning and memory function. Spectrophotometry was employed to determine the content of thiobarbituric acid-reactive substances (TBARS) and the activities of antioxidative enzymes in the brain. The present results demonstrate that D-galactose-induced amnesic mice had signir cantly decreased learning and memory function. The reduced activities of superoxide dismutase and glutathione peroxidase and increased levels of TBARS were found in brain tissue of the amnesic mice. Melatonin, administered (ig) at doses of 0.1, 1, or 10mg/kg to the D-galactose-treated mice for 3 months, was su