The 37-kDa immunoreactive band, identified as rat APE1/Ref-1 using liquid chromatography/tandem mass spectrometry in lipopolysaccharide-induced endotoxemic rats [12], suggests that plasma APE1/Ref-1 level may serve as a serological biomarker for endotoxemia. This evidence concerns the gene APEX1 and serum lipopolysaccharide activity.