We studied here the long-term maintenance of distinct populations of T helper type 1 (T_H1)-lineage cells in vivo and found that effector T_H1 cells, defined by their secretion of interferon-γ (IFN-γ), are short-lived and do not efficiently develop into long-term memory T_H1 cells. In contrast, a population of activated T_H1-lineage cells that did not secrete IFN-γ after primary antigenic stimulation persisted for several months in vivo and developed the capacity to secrete IFN-γ upon subsequent stimulation. These data suggest that a linear differentiation pathway, as defined by the transition from IFN-γ–producing to resting memory cells, is relatively limited in vivo and support a revised model for T_H1 memory differentiation.