8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dGuo) is among the most common reactive oxygen species-induced DNA lesions and can be used as a biomarker for oxidative stress. The lesion has been linked to several biological processes and diseases, including colorectal cancer, Huntington’s disease, estrogen-induced gene expression, and thymine dimer repair (reviewed in Delaney et al., 2012). The following assay is used to quantify 8-oxo-dGuo levels in DNA as described in Sousa et al. (2013).