Human epidermis was separated from dermis by means of a suction blister device and dissociated with trypsin. The epidermal cell (Ec) suspensions contained 2-6% Langerhans cells (Lc). Using a new rosette technique for enrichment of Lc, suspensions were obtained that contained 50-92% viable Lc. Ec, enriched Lc, or peripheral blood monocytes (Mo) were cocultured with or without antigens (Candida albicans, herpes simplex virus) and autologous T lymphocytes from sensitized donors. Strong proliferative T-cell responses were obtained provided Ec, enriched Lc, or Mo were also present. Furthermore, Lc were more effective than similar numbers of Mo in inducing T-cell responses to the antigens tested, and Lc did not require the presence of significant numbers of keratinocytes to exert this function.