T-cell receptor gene rearrangement using a C beta probe was evaluated in 12 patients with rheumatoid arthritis, 2 with juvenile rheumatoid arthritis, and 1 with systemic lupus erythematosus, and in all the samples a dominant T-cell receptor gene rearrangement was noted. In rheumatoid arthritis identical T-cell receptor gene rearrangement was noted in freshly isolated synovial tissue-infiltrating lymphocytes (TIL) and the corresponding interleukin 2-propagated culture. TIL from five different joints obtained from one rheumatoid arthritis patient shared one dominant band, and TIL from three joints had an identical rearrangement. Limiting dilution experiments showed that 10% of T-cell clones had rearrangements matching the corresponding bulk in one rheumatoid arthritis patient. These findings lend further support to the suggestion that the clonal dominance noted among synovial tumor-infiltrating lymphocytes is the result of an in vivo process reflecting a selective T-cell receptor gene usage.