BrdU (5-Bromo-2-Deoxyuridine) is a derivative of uridine that can substitute for thymidine during DNA synthesis. The detection of BrdU incorporation into DNA is a common method to quantify newly synthesized DNA and to identify cells in the S-phase of the cell cycle. BrdU incorporation is frequently used in proliferation assays to study DNA repair, sister chromatid exchange, and the cytokinetics of normal and neoplastic cells.