Flow cytometry of synchronized NHF1 cells. Cells were grown to confluence arrest and replated at low density in the presence of aphidicolin and BrdUrd as described. After 24 hrs cells were collected and analyzed by flow cytometry. The ordinate of this graph shows BrdUrd incorporation as indicated by fluorescently-labeled anti-BrdUrd antibody and the abscissa shows DNA content as indicated by propidium iodide staining. The boxes outline areas that were analyzed for cell number.