It has recently been demonstrated that CD48, which is expressed on T cells, B cells, thymocytes and splenocytes, is a ligand for mouse CD2 and that it can function as one of the costimulatory molecules in the activation of T cells. In this study, we examined the expression of CD48 on epidermal Langerhans cells (LC), which are potent antigen-presenting cells in the skin. Both freshly isolated and short-term-cultured LC were shown to express CD48 by flow cytometry. In contrast to most of the adhesion molecules expressed on LC, CD48 expression on short-term-cultured LC did not differ significantly from that on freshly isolated LC. We also examined the contribution of CD48 to antigen presentation by LC. We stimulated the myoglobin-specific T-cell clone, TK.G4, and allogeneic splenic T cells with freshly isolated LC and cultured LC, respectively, in the presence of various concentrations of anti-CD48 monoclonal antibody (mAb). Even at the concentration of 30 micrograms/ml, however, the anti-CD48 mAb did not show any inhibitory effects on either allogeneic or antigen-specific T-cell proliferation, whereas at a concentration 10 micrograms/ml, the anti-CD48 mAb significantly suppressed the proliferation of spleen cells stimulated with phytohaemagglutinin (PHA). These findings show that LC persistently express CD48, although its direct role in antigen presentation has not yet been clarified in vitro.