Antigen specificity of the antibodies differentially labeling 5-chloro-2-deoxyuridine (CldU) and 5-iodo-2-deoxyuridine (IdU). C57BL/6 mice were loaded with CldU only (A–C), IdU only (D–F), or with 5-bromo-2-deoxyuridine (BrdU; G–I). Sections from the kidneys of these mice loaded with different deoxyuridines were stained for detecting the presence of both CldU (using rat anti-BrdU; Abcam, Cambridge, MA; red stain) and IdU (using anti-BrdU antibody; Biosciences Pharmingen, San Jose, CA; green stain). Within each row of images, white arrows indicate the position of the same nuclei. Merged images (including the nuclei identified by DAPI label) demonstrate that these antibodies independently identify CldU (A–C) and IdU (D–F) within nuclei of the outer medulla. Both antibodies identify the presence of BrdU (G–I).