Bcl-2 plays a critical role in regulating cell survival and apoptosis. We examined Bcl-2 expression in virus-specific CD8 T cells during the expansion, death, and memory phases of the T celt response following infection of mice with lymphocylic choriomeningitis virus (LCMV). Naive CD8 T cells expressed a basal level of Bel-2 that was down-regulated in effector CD8 T cells just before the death phase. Bcl-2 levels remained low surviving memory CD8 T cells expressed higher levels of Bcl-2 than naive cells. These changes were shown to occur in LCMV TCR transgenic cells as well as virus- specific CD8 T cells in C57BL/6 and BALB/c mice identified by MHC class I tetramers. In all instances, memory CD8 T cells expressed higher levels of Bcl-2, suggesting that increased Bcl-2 expression plays a role in the long- term maintenance of memory CD8 T cells in vivo.