Cell cycle analysis of freshly isolated peripheral blood CD34⁺-selected cells (day 0) and the same cells after 3 days of stimulation with IL-3, IL-6, and SCF (day 3) as detailed in the Materials and Methods. Cells were stained with propidium iodide and analyzed on an Epics-Elite flow cytometer (Coulter Electronics). The percentages of cells within G₀/G₁, S, and G₂/M phases of the cell cycle are indicated. DNA histograms are representative of five experiments.