We are investigating the functions of the Thy-1+ dendritic cells present in murine epidermis. Dendritic epidermal Thy-1+ cell (DETC) lines conjugated in vitro with hapten induce specific immunologic tolerance upon intravenous (i.v.) or subcutaneous injection into the footpad of normal mice. In these studies, we demonstrate that hapten-conjugated cells of other long-term, interleukin-2 (IL-2)-dependent, T cell lines are unable to induce tolerance upon footpad injection, indicating that the ability of DETC lines to induce tolerance is not a function of long-term cell culture or IL-2 dependence. Suppressor T cells were not found in mice made tolerant by footpad injection of hapten-conjugated cells of the DETC line AU16, although they could be demonstrated in mice made tolerant by i.v. injection. Studies of lymphocyte proliferation in vitro suggested that hapten-conjugated AU16 cells may induce tolerance by inhibiting the proliferation of activated T lymphocytes.