This study was conducted to investigate whether a moderate running exercise would enhance or prevent the lipid peroxidation in animal body and also stimulate or depress the degradation-excretion of lipid peroxides (LIPOX, thiobarbituric acid reactive substances determined as malon dialdehyde) in young female rats. Compared with sedentary rats, voluntary wheel-running exercised rats did not show any significant difference in total LIPOX contents in plasma and several tissues including brain, and whole body during 4 weeks of experiment with a vitamin E-free low LIPOX diet. On the contrary, when rats were previously fed a high LIPOX diet and then allowed voluntary exercise with a vitamin E-added low LIPOX diet, total LIPOX contents per whole body reduced significantly faster in the exercised rats than in the sedentary controls during 2 weeks of exercise. At that period, LIPOX were progressively increased in the brain in both groups of animals, but was significantly greater in the exercised group. Interestingly, more than 80% of total LIPOX contents in whole body were found to be stored in carcass portions regardless of greater or lesser amounts of LIPOX contents in rats. These data suggest that a moderate exercise of several weeks might enhance the degradation-excretion of LIPOX but not the formation-accumulation of LIPOX in rats. Exercise also seems to modulate LIPOX transference among tissues.