S phase-enriched Lin⁻ Rho^low/Ho^low cells arrested in subsequent G₀ /G₁ phase by isoleucine-deprivation re-enter proliferative cycle after the release from isoleucine-block. Thirty hours after cytokine stimulation, Lin⁻ Rho^low/Ho^low cells were subjected to isoleucine-deprivation for 36 hours as described in the Materials and Methods. The cells were then released from isoleucine-block and at indicated intervals duplicate aliquots of cells were labeled with ³H-thymidine and processed for autoradiography to assess the percentage of cells with labeled nuclei as described in the Materials and Methods.