Combined loss of Bim and Bmf renders B cells independent of survival-promoting cytokines and refractory to BCR ligation-induced apoptosis. Transitional T1 (sIgM^highCD21^low) or T2 (sIgM^highCD21^high) B cells were sorted from spleens of 8- to 10-week-old mice of the indicated genotypes and placed in culture. Cells were either (A,C) left untreated or (B,D) stimulated with plate-bound anti-IgM F(ab)₂ fragments for 48 hours. (E-F) Follicular (FO) B cells (CD21⁺CD23⁺) or plasma cells/plasmablasts (PC/PB) (B220^+/lowCD138⁺) were sorted from spleens of mice of the indicated genotypes and placed untreated in culture. Cell viability was assessed after 24 and/or 48 hours by flow cytometric analysis. Data are presented as means ± SEM of ≥3 independent experiments and 3 to 5 animals per genotype. Significant differences (P < .05) are indicated *between WT and Bmf^−/−, **between WT and Bim^−/−, ^#between WT and DKO, and ^§between Bim^−/− and Bim/Bmf DKO mice.