8-Oxo7,8-dihydro-2′-deoxyguanosine (8-oxodG), an oxidized form of deoxyguanosine, is a major product of DNA oxidation and is used as a biomarker for oxidative stress in cancer. The level of 8-oxodG in cellular DNA reflects the balance between the rate of DNA damage and the efficiency of DNA repair. This merged image of double fluorescent-labeled murine xenografted human kidney cancer cells shows a high abundance of 8-oxodG (stained green with FITC) within the nuclei (identified by red propidium iodide staining of all DNA). A higher level of orange to green staining within the kidney tumor section as compared with the normal kidney (not shown) indicates more oxidative DNA damage within the tumor. The image was taken using a Nikon research microscope equipped for epifluorescence with excitation and band pass filters. For details, see article by Abu Aboud and colleagues on page 6746.