Deletion of Rac1/Rac2, but not Rac1 alone, in T cells results in decreased T-lymphocyte cellularity in spleen that is associated with decreased T-cell proliferation, adhesion, and migration and increased apoptosis. Lck-Cre–targeted mice were injected intraperitoneally with BrdU (100 μg/g body weight) 12 hours prior to spleen harvest. The isolated splenocytes were counted and stained with anti-CD4, -CD8, -TCRβ, and -BrdU antibodies or annexin V followed by flow cytometry analysis of the CD4/CD8 subpopulations (A), the proliferating cells (B), and the apoptotic cells (C) in various T-cell subpopulations. The purified splenic T cells were also assayed for adhesion to fibronectin and for migration toward SDF-1α (D). WT, n = 10; Rac1^−/−, n = 6; and Rac1^−/−Rac2^−/−, n = 6. *P < .05; **P < .01. Error bars represent SD.