Synovial T cells play a crucial role in the pathogenesis of rheumatoid arthritis (RA) synovitis. We have quantitatively analyzed the T cell receptor (TcR) variable (V) region gene repertoire of freshly isolated synovial fluid (SF) T cells, comparing it with that of peripheral blood (PB) T cells in RA. The TcR V gene repertoire of PB and SF T cells in RA and osteoarthritis was heterogeneous. In contrast, V alpha 11 in SF was expressed to a greater degree in three of five RA patients, and increased levels of V beta 6, 1-3 were found in the SF of four of six RA, compared with paired PB. Of note, V beta 6, 1-3 was universally used in four RA patients with a disease duration of less than 10 years, irrespective of their HLA-DR types. This was in contrast to two other RA patients, suffering for more than 20 years, who showed different V alpha and V beta usages. beta-chain sequence analysis in RA patients with a preference for V beta 6, 1-3 has shown that a few clones dominated in SF, whereas polyclonality was observed in PB. These findings suggest oligoclonal expansion of T cells in response to specific antigen(s) in the SF of these patients with RA of relatively short duration. Concomitant use of two hydrophobic amino acids, leucine and valine in the D beta region was noticeable among the predominant SF clones. These two amino acids might directly contact a peptide specific for the induction of synovitis in RA patients. TcR-directed therapy may, therefore, be useful for the treatment of early RA synovitis.