Pineal graft from young to old rats was performed and red blood cell hemolysis, induced by the water-soluble radical initiator 2,2'-azobis (2-amidino-propane) dihydrochloride (AAPH), was evaluated 6 months after graft. Pineal graft modified the hemolysis curve kinetic profile in grafted rats versus age-matched controls, the 50% hemolysis time as well as the lag time were longer, whereas the maximal amount of hemolysis was lower, and it occurred over a longer period of time. Thiobarbituric acid reactive substances production was lower in pineal-grafted rats than in controls and the age-related decrease of erythrocyte membrane fluidity was prevented by pineal graft. The present findings support an important physiological role of pineal gland in preventing age-related alterations of erythrocyte membranes and suggest a possible antioxidant action of melatonin.