I dentification of expanded clones engaged in immune and autoimmune responses is still imperfect, since they are often diluted by irrelevant cells expressing diverse specificities. To efficiently characterize T cell receptors expressed by clonally expanded lymphocytes in rheumatoid arthritis (RA) and other inflammatory conditions, we developed an assay system, termed sequence enrichment nuclease assay (SENA). Key elements of SENA are the efficiency of heat-denatured DNA strand reassociation, which increases exponentially with concentration, and the elimination of unhybridized sequences by single-strand-specific DNase. T cell clonal expansions were identified primarily in synovial fluids, but also in peripheral blood of RA patients. Synovial fluids had more prominent expansions in the CD8 than the CD4 subset, whereas clonal expansions in the CD4 subset predominated among peripheral blood lymphocytes. Dominant clones exhibited diverse sequences with no clear conservation of junctional motifs, although the same amino acid sequence was identified in two patients. In most instances, dominant clones in the blood were discordant to those in the corresponding synovial fluid, suggesting local stimulation or preferential sequestration of T cells displaying particular specifities.