Bromodeoxyuridine (5-bromo-2-deoxyuridine, BrdU) is a synthetic nucleoside analogue of thymidine. BrdU is commonly used to detect cell proliferation.
BrdU is phosphorylated by cells to BrdUTP. This precursor is incorporated into newly synthesised DNA during S phase instead of deoxythymidine triphosphate (dTTP). It can then be detected with an anti-BrdU antibody coupled to a fluorophore or an enzyme. Other detection methods included BrdU quenching of DNA fluorophores and selective photolysis of BrdU-containing DNA.