Progression of cytokine-stimulated Lin⁻/Sca⁺ cells through G₁ and into S phase of cell cycle. Lin⁻/Sca⁺ cells were incubated in medium containing SCF alone, SCF plus IL-3, or a cocktail of 7 cytokines (IL-3, IL-1α, GM-CSF, G-CSF, SCF, FGF, and CSF-1), and at indicated intervals duplicate aliquots of cells from each group were analyzed for ³H-thymidine incorporation followed by autoradiography to assess the percentage of cells with labeled nuclei as described in the Materials and Methods.