A great deal of attention has been focused on the possible therapeutic implications of lipoic acid as a potent antioxidant. Lipoic acid serves as a vital cofactor for α-keto-acid dehydrogenase and is well known for its free radical-quenching effect. We evaluated the age-associated alterations in membrane-bound enzymes, glutathione and lipid peroxidation in young and aged rats in response to lipoate supplementation. In aged rats, the level of glutathione and the activities of membranebound enzymes were lower, whereas thiobarbituric acid reactive substances (a marker of free radical damage) were higher than those in the young rats. Intraperitoneal administration of lipoic acid to the aged rats led to a time-dependent reduction in lipid peroxidation and elevation in the activities of membrane-bound enzymes as well as in the level of glutathione. Our observations highlight the protective effect of lipoic acid in age-associated free radical-induced oxidative stress, thus proving its efficacy as a potent antioxidant.