BrdU is a uridine derivative and a structural analog of thymidine that can be incorporated into DNA during the S-phase of the cell cycle as a substitute for thymidine. Cells can be pulse-labeled with BrdU and analyzed with antibodies against BrdU to determine the proportion of cells in the S-phase of the cell cycle during a given interval. The MoBU-1 antibody is useful for the detection of incorporated BrdU by fluorescent cell staining (ICFC), flow cytometry, and immunohistochemistry.