CD150 marks a population of more quiescent HSCs. SP^KLS cells fractionated based on position within the SP (Hoechst Blue fluorescence) and CD150 expression (gates i-iv) were isolated from mice treated with the nucleotide analog BrdU for 3 days and examined by flow cytometry for BrdU incorporation, an indicator of transition through the cell cycle. CD150⁻ SP^KLS cells were substantially more proliferative in vivo than their CD150⁺ SP^KLS counterparts, with the lower SP being generally less in cell cycle than the upper SP. Percentages shown correspond to the gated proportion of the plot.