Bone marrow (BM) and blood (pooled from 20 mice in experiment 1 and 10 mice in experiments 2 and 3) were obtained from animals treated with BrdU and CY/G-CSF (day + 4) and prepared for flow cytometry. Progenitors were double-sorted onto glass slides coated with tissue adhesive. Cells were lysed, and DNA was denatured and stained with anti-BrdU antibodies, which were visualized by immunofluorescence microscopy (see “Materials and methods”). BrdU⁺ and BrdU⁻ cells were scored, and ratios were made of BrdU⁺ cells/total cells counted. The mean of the 3 BM experiments is expressed ± SD.