The involvement of Lyt-2+ T cells in the immunological control of cutaneous leishmaniasis was assessed by studying the course of the disease in mice in which the number of these cells was reduced by treatment with anti-Lyt-2 monoclonal antibody (mAb). Administration of anti-Lyt-2 mAb exacerbated Leishmania major-induced cutaneous lesions in both genetically resistant and susceptible mice. This effect correlated with a drastic reduction in the number of specific Lyt-2+ T cells generated during infection. These results, together with the observation that resistant mice possess higher numbers of specific Lyt-2+ T cells in lymph nodes draining their lesions than susceptible mice, 3 weeks after infection, indicate that Lyt-2+ T cells also play a role in the immunological control of Leishmania major-induced lesions.