Cell cycle analysis of human B-cell subpopulations reveals IgD+CD38−CD23−FSChi (CD71+) cells are in G1 phase of the cell cycle. B-cell subpopulations were separated as described previously1,2 with the addition of IgD+CD38−CD23−FSChi cells described here. Cell cycle status was determined by flow cytometry of Hoechst 33342– and pyronin Y–stained populations. The diagram at the side illustrates how actively dividing cells can be resolved on the basis of RNA/DNA staining into G1 or S + G2 + M fractions.