Leishmaniasis is caused by infection with the protozoan parasite, Leishmania, that parasitizes human cells, and the cellular immune response is essential for controlling infection. In order to measure the host T cell response to Leishmania infection, we have measured the expansion, activation state and functional potential of specific T cells as identified by their T cell receptor Vb region expression. In a group of cutaneous leishmaniasis (CL) patients, we evaluated these characteristics in nine different T cell subpopulations as identified by their Vb region expression, before and after specific Leishmania antigen stimulation. Our results show: (1) an increase in CD4+ T cells expressing Vb 5•2 and Vb 24 in CL compared to controls; (2) a Leishmania antigeninduced increase in CD4+ T cells expressing Vb 5•2, 11, 12 and 17; (3) a profile of previous activation of CD4+Vb 5•2-, 11- and 24-positive T cells,with higher expression of CD45RO, HLA-DR, interferon-g, tumour necrosis factor-a and interleukin-10 compared to other Vb-expressing subpopulations; (4) a positive correlation between higher frequencies of CD4+Vb5•2+ T cells and larger lesions; and (5) biased homing of CD4+ T cells expressing Vb 5•2 to the lesion site. Given that CL disease involves a level of pathology (ulcerated lesions) and is often followed by long-lived protection and cure, the identification of specific subpopulations active in this form of disease could allow for the discovery of immunodominant Leishmania antigens important for triggering efficient host responses against the parasite, or identify cell populations most involved in pathology.