Whether the L-selectin-low (L-sel-lo) phenotype of acutely stimulated CD8+ T cells is a permanent characteristic of long-term memory CTL precursors (p) is addressed for mice primed with an influenza A virus or the murine parainfluenza type 1 virus, Sendai virus. In both cases, many of the splenic CD8+ CTLp gradually lose the predominantly L-sel-lo profile associated with recently generated CTLp populations. The influenza-specific CTLp also tend to revert from the activated alpha 4-integrin-high to the resting alpha 4-integrin-low form. The kinetics of the switch back to the "naive" L-sel-hi phenotype differs for the influenza and Sendai virus models, perhaps reflecting events occurring during the acute phases of these responses. The return to being L-sel-hi is not due to irreversible lymphocyte senescence, because restimulation of this set with the inducing virus in vitro causes most of the cells to become L-sel-lo. Also, despite the time-related drift of these particular memory CTLp to the L-sel-hi state, the size of the total pool of L-sel-lo CD8+ T cells increases with age.