The oxidative injury in Alzheimer's disease (AD), in which amyloid beta protein induces production of reactive oxygen species, may be cause of neurodegeneration. APE1/Ref-1 is a protein involved in DNA repair and in redox co-activating function over different transcription factors. We investigated by immunohistochemistry using a highly specific monoclonal antibody, the localization of APE1/Ref-1 in autoptic and bioptic AD brain tissues in comparison with brains with unrelated pathological or normal conditions. Reliable APE1/Ref-1 immunostaining was obtained in biopsies, but not in autoptic tissues. An increased nuclear expression of APE1/Ref-1 in AD cerebral cortex supports the view that the cellular adaptive response to the oxidative stress condition is involved in the pathogenesis of this disease.