The levels of lipofuscin and lipid peroxidation reflect the degree of free radical-induced oxidative damage in the brain. We examined the effects of CDA-II, a preparation of human urine, on lipofuscin and lipid peroxidation in the brain of young (3.5 months) and middle-aged rats (17 months). The rats were given CDA-II orally at dosages of 0.3 or 1.0 g/kg daily for 8 weeks. CDA-II significantly suppressed the contents of lipofuscin and lipid peroxidation in both young and middle-aged rats. CDA-II also elevated the activity of superoxide dismutase, and the amounts of glutathione and ascorbic acid in the middle-aged rats, but not in the young ones. Our results suggest that the protection against oxidative damage by CDA-II in the young rat brain may be due to its scavenging activity against free radicals. In the middle-aged rats, in addition to the scavenging activity, the levels of endogenous antioxidants were also enhanced by the CDA-II treatment.