OxodG and Fapy center dot dG are two frequently formed DNA lesions that affect replication in vitro and in cells. They are also potentially important biomarkers for determining the effects of oxidative stress and aging in cells. We report the first method that enables one to selectively detect and individually quantify Fapy center dot dG and OxodG in DNA. The method relies upon selective chemical trapping of oxidized forms of the lesions with a biotinylated derivative of spermine. Selectivity for OxodG over Fapy center dot dG is achieved by varying the oxidant. The covalently tagged lesions are quantified using a fluorescence assay that is carried out in microtiter plates. The fluorescence assay is generally applicable to quantifying DNA lesions that can be tagged with biotin.