Memory T cell (TM) populations specific for transplantation Ags may arise from sensitization due to blood transfusions, tissue transplants, or in multiparous females. In each of these scenarios, TM cells are likely generated, and have been shown to persist in such individuals for extended time periods. Heightened resistance to allogeneic marrow engraftment in certain individuals is therefore consistent with the presence of antidonor TM. CD8 TM were generated against a single minor H Ag (MiHA) epitope to determine if such cells could inhibit allogeneic marrow engraftment. The present results demonstrate that B6 mice sensitized to a single immunodominant (H60) epitope efficiently reject donor marrow allografts expressing this MiHA alone or together with multiple minor transplantation antigens, even following ablative TBI conditioning. To further address the survival and function of these CD8 TM, sensitized mice were ablatively conditioned and administered a syngeneic HCT. CD8(+)H60(TCR+) TM were clearly detected up to 2 weeks later in such recipients. Additionally, the memory cells present were capable of mediating effector responses as evidenced by their ability to resist a second, allogeneic HCT. In summary, these observations highlight the increased risk of resistance in the presence of antidonor antigen-specific CD8 TM due to their ability to survive and function even following rigorous conditioning and HCT.