Hypersensitivity to a streptococcal antigen is postulated to be the pathogenesis of Behçet's disease. We analyzed T lymphocyte-phenotypes infiltrated in cutaneous pustular lesions in Behçet's disease and found that CD4+ T cells were predominant components although CD8+ T cells were also present in the lesion. In addition, we established T cell lines from pustular lesions of the four patients with a streptococcal antigen, KTH-1. Two of the cell lines showed the cell surface markers of CD8+TCR alpha beta +, and expressed mRNAs for interleukin (IL)-8, tumor necrosis factor (TNF) alpha, and perforin. Two other T cell lines expressed the cell surface markers for CD4+TCR alpha beta +. Cytokine expression pattern of the two CD4+ T cell lines revealed that one is Th1 type and the other is Th2 type. The Th2 type cell line showed marked proliferation with autologous peripheral blood mononuclear cells, suggesting that the self-reactive T cells play some role on the pathogenesis of Behçet's disease.