One of the mechanisms underlying the aging process is proposed to be oxidative damage by free radicals. Carnosine (β-alanyl-L-histidine) is a dipeptide with antioxidant properties. In this study, we investigated the effect of carnosine supplementation on oxidative stress in serum, apoB-containing lipoproteins (LDL + VLDL) and erythrocytes of young and aged rats. At the initiation of the study, young and aged rats were 5 and 22 months old, respectively. Carnosine (250 mg/kg, daily, i.p.) was administered for 1 month to young and aged rats. We found that serum malondialdehyde (MDA) and diene conjugate (DC) levels and endogenous DC and copper-induced MDA levels in the LDL+ VLDL fraction increased in aged rats, but there was no change in plasma antioxidant activity. Endogenous DC and H(2)O(2)-induced MDA levels were also higher, but glutathione (GSH) levels were lower in erythrocytes of aged rats. Administration of carnosine for 1 month to aged rats resulted in decreased levels of MDA and DC in serum, the LDL + VLDL fraction and erythrocytes and increased levels of GSH in erythrocytes. Our findings indicate that in vivo carnosine treatment may be useful for the decrease in aged-induced oxidative stress in serum, the LDL + VLDL fraction and erythrocytes.