Synovial fluid (SF) mononuclear cells from a patient with Chlamydia trachomatis induced acute Reiter's disease were directly by limiting dilution in a representative protocol using phytohemagglutinin in the cloning medium. Out of 76 alpha beta-TCR+ CD4+ T lymphocyte clones, 7 were shown to specifically recognize C. trachomatis in a proliferation assay. The antigen recognition of these clones was HLA-DP restricted. Unexpectedly, 2 HLA-DR restricted clones showed a proliferative response to Yersinia enterocolitica O3, though the patient had no history of yersinia infection. The high frequency of SF derived T cells with specificity for species-specific chlamydial antigens and the limited diversity of HLA class II restriction of these clones may indicate an oligoclonal synovial T cell response to persistent intraarticular chlamydia.