Cytotoxic T lymphocytes (CTL)5 of female origin that readily lysed syngeneic male lymphoid cells in specific, dose-dependent, H-2 restricted fashion had little or no activity against syngeneic male epidermal cells (EC) in short-term or long-term chromium-release assays. Moreover, although male EC were quite capable of priming syngeneic female lymphocytes in vivo for the accelerated rejection of male-specific skin grafts and for the subsequent generation of H-Y-specific CTL by exposure of primed female spleen cells (SC) to irradiated, syngeneic male SC in vitro, male EC themselves were incapable of stimulating the development of H-Y CTL when cocultured with primed female SC. Tests of EC from reciprocal male-female radiation chimeras revealed that keratinocytes, not marrow-derived EC (Langerhans cells), were responsible for the priming ability of EC in vivo. Moreover, H-Y antigen was serologically defined on EC that failed to express H-Y-specific CTL target-cell determinants. Alternative explanations of these findings are discussed, including the possibility that the inability of H-2-restricted T cells to lyse male EC results from the lack of association of H-Y antigen and H-2 restricting elements on the EC membrane.