We have examined synovial fluid (SF) T cells from 5 children with various types of juvenile arthritis. Using the polymerase chain reaction (PCR) to determine the expression of 20 individual T cell receptor (TCR) beta variable (V) region families, we have shown with each patient that the SF T cells are polyclonal. Nevertheless, expanded usage of some families by SF T cells relative to peripheral blood T cells was evident in some cases. We conclude that the pattern of T lymphocytes in the inflamed joint may be a consequence in part of a polyclonal expansion or nonspecific homing of T cells to the joint, and in part a more restricted expansion of T cells potentially driven by arthritogenic antigens.