Bromodeoxyuridine (BrdU) is a thymidine analog that incorporates DNA of dividing cells during the S-phase of the cell cycle. Once incorporated, these nucleoside analogs serve as cell cycle and proliferation markers that can be detected using labeled probes to identify cells that are actively proliferating.

Alternatives, such as Bucculite™ dU reagent, are now available for cell cycle analysis with shorter and simpler protocol than that required for BrdU.