Loss of endogenous Bcl-2 does not affect the enhanced proliferation of Eμ-myc transgenic B lymphoid cells. Donor-derived pro-B cells (Ly5.2⁺ B220⁺ sIg⁻ c-Kit⁺) and pre-B cells (Ly5.2⁺ B220⁺ sIg⁻ c-Kit⁻) were purified by multiparameter cell sorting from the bone marrow of mice reconstituted with wt, bcl-2^−/−, Eμ-myc, and Eμ-myc/bcl-2^−/− cells. The purified cells were then permeabilized and stained with PI, and their DNA content was analyzed by flow cytometry. The average percentages of cells in the G₀/G₁ and S/G₂/M phases, obtained by manual gating, are indicated in the top right corners of the histograms. Results are representative of 3 to 4 independent experiments from 3 to 5 mice of each genotype.