Three mAb to variable region determinants of the alpha/beta-chain TCR were used to detect discrete populations of peripheral blood T cells. T cells sharing a TCR determinant defined by such an antibody presumably use the same or similar TCR V or J genes for their alpha- or beta-chains. Thus analysis with these mAb provides a tool to investigate TCR gene usage and expression. Since autoantigen specific T cells may play an important role in initiating autoimmune diseases, TCR were analyzed in different autoimmune diseases and control groups including rheumatoid arthritis, Graves disease, idiopathic thrombocytopenic purpura, psoriasis, SLE, insulin-dependent diabetes mellitus, and in nonautoimmune control diseases and normals. Purified T cells were stained by indirect immunofluorescence with three mAb to TCR variable regions: mAb S511 stains 1.8 +/- 0.9% (mean +/- 2 SD), mAb C37 stains 3.4 +/- 1.5% and mAb OT145 stains from 0 to 6% of T cells from normal donors. Several individuals were identified with expanded subsets of positive T cells. One patient with adult ITP followed during a 12-mo period consistently had elevated percentages of T cells staining with the mAb OT145 (15.9 to 24.5%). These cells were found to be exclusively CD8+. By Southern blotting DNA prepared from these OT145+, CD8+ cells, but not DNA from the patient's OT145- T cells, revealed a clonal rearrangement using a beta-chain C region probe. Thus this patient had a monoclonal expansion of CD8+, OT145+ cells. Hyperexpression of a TCR variable region, as defined by the available mAb, could not be associated with any of the diseases studied. Examination of T cells at the site of autoimmunity, such as T cells from rheumatoid arthritis synovial fluid, revealed normal percentages of cells staining with these mAb. Immunoperoxidase staining of psoriatic lesional skin showed no striking enrichment of T cells bearing one or the other TCR type.