Apolipoprotein E (apoE) is predominantly a lipid transport protein involved in membrane repair and synaptic plasticity in brain. Its genotype is associated with late-onset sporadic and familial Alzheimer's disease (AD). Its expression increases when any injury takes place in the nervous system and in age-related disorders including AD. However, it is not clearly understood how the level of apoE changes in the normal aging brain. Therefore, we have analyzed the effect of age on apoE protein and mRNA level in the cerebral cortex of young, adult, and old male AKR strain mice. Western, northern, and RT-PCR results reveal that the level of apoE protein and mRNA is higher in young as compared to adult and then remains unchanged in old mouse cerebral cortex. This indicates that during normal aging, apoE level is maintained in old similar to adult and suggests involvement of other factors in maintaining apoE-mediated brain functions in old.