Langerhans (LC) cells require incubation with protein antigen for several days before the cells effectively stimulate proliferation of cloned, H-2 restricted, antigen-specific T h cells. In contrast, splenic antigen-presenting cells are immediately effective. LC are immediately competent, however, if an immunogenic peptide rather than the intact protein is the immunogen, indicating that resident or unchallenged LC have the required class II MHC and can provide the signals necessary for T-cell proliferation but may lack the capacity to internalize or cleave protein antigens. We propose that delayed antigen presentation by LC may be intrinsic and advantageous for promoting early systemic immunity. LC stimulate cloned T h1 and T h2 cells equally well, suggesting that LC may not limit or bias the type of immunity that occurs with cutaneous antigenic challenge.