Cytokine-stimulated Lin⁻ Rho^low/Ho^low cells in first S phase are blocked in subsequent G₀ /G₁ phase by isoleucine-deprivation. Lin⁻ Rho^low/Ho^low cells were incubated in medium containing a cocktail of 4 cytokines (IL-3, IL-6, IL-11, and SCF ) at 37°C in a humidified incubator with 5% CO₂ . Thirty hours later, when about 60% of the cells are in S phase, the total culture was divided into two groups of equal cell number. One group of the cells was maintained in the same media as described above and the other group of cells was subjected to isoleucine-deprivation as described in the Materials and Methods. At indicated intervals, 200-μL aliquots of cells from each group were analyzed for the percentage of labeled nuclei as described in the Materials and Methods.