We measured previously the lipid hydroperoxides level in the brain and peripheral organs such as heart, liver, lung and kidney of senescence acceIerated-prone (SAMP8) and -resistant(SAMR1) mice at 3,6 and 9 months of age. It was found that the lipid hydroperoxide leve1s in the brain did not show any age-dependent change, and that they Were significantly higher in SAMP8 than in SAMR1 over the defined periods. In contrast, the lipid hydroperoxide leve1s in the peripheral organs, including liver, Were increased with aging in both substrain, and they were significantly higher in SAMP8 than in SAMR1 at 3 and 6 months of age. In addition, the lipid hydroperoxide levels in the peripheral organs were higher than those in the brain in both substrains. To elucidate the difference of lipid hydroperoxide levels between the brain and the peripheral organs, we further carried out lipid component analysis in the brain and liver, one of the peripheral organs, of SAMP8 and SAMR1 at 6 months of age.