To investigate whether Langerhans cells are capable of inducing contact sensitivity effector T cells, we incubated purified T cells from naive mice with syngeneic cultured trinitrophenyl-modified Langerhans cells for 4–5 d. The cells were then expanded in interleukin-2 and fresh medium for another 6–9 d and injected intravenously into naive syngeneic recipient mice. After the ears of recipient mice were painted with 1% trinitrochlorobenzene, we observed an ear-swelling response peaking at 24–48 h. The ear-swelling response was hapten specific. CD8- but not CD4-depleted T cells mediated strong contact sensitivity. Systemic adoptive transfer into nude mice also lead to a hapten-specific delayed ear-swelling response. However, this response was less protracted than in euthymic animals, suggesting the participation of the recipient (non-immunized) T cells in the ear-swelling response of the euthymic mice. Lymphokine analysis of in vitro primed and restimulated T cells revealed predominant production of interleukin-2 but little or no interleukin-4. These in vitro primed cells therefore resemble type I or inflammatory T helper cell clones.