In the present study we chose to develop a murine model of Langerhans cell (LC) free epidermal cell (EC) cultures. EC were cultured in low Ca medium which results in the replication of epidermal basal cells (EBC) without stratification and differentiation. By immunofluorescence techniques using anti I-A monoclonal antibodies (mAb), LC were never detected within EBC after a 7-day culture period. Unexpectedly, when spleen-enriched T cells were added to the I-A negative EBC, a strong proliferative response occurred. The proliferating spleen cell population was Thy 1+ and, in large part, L3T4+. Syngeneic responses were as strong as allogeneic responses, which is further evidence that residual LC could not account for the observed effect. Furthermore, in vitro T cell proliferation on EBC was unable to be inhibited by the addition of anti I-A mAb during a mixed skin lymphocyte reaction. Supernatants from EBC failed to induce T cell proliferation, suggesting the absence of a soluble mitogenic factor released from EBC. The findings present evidence that murine LC depleted EBC can trigger lymphocyte proliferation through an yet, undefined stimulus.