Objective. To investigate whether Fas-mediated apoptosis has potential as a new therapeutic strategy in rheumatoid arthritis (RA) by use of a novel model of' RA in which human RA tissue is grafted into SCID mice. Methods. Fresh rheumatoid synovial tissue including joint cartilage was grafted subcutaneously into the backs of SCID mice. Six weeks after engraftment, anti-Fas monoclonal antibody was injected intraperito-neally. Time-related apoptotic changes caused by anti-Fas monoclonal antibody in grafted synovium were evaluated by nick end-labeling histochemistry. Results. Thirty-six hours after the injection, diffuse apoptotic changes were observed in the grafted synovia. Four weeks after the injection, rheumatoid synovial tissue diminished. ConcZusion. This is the first report concerning the present effectiveness of anti-Fas monoclonal antibody in diminishing rheumatoid synovium in vivo, and suggests the possibility of a new strategy for treating rheumatoid arthritis by inducing Fas-mediated apoptosis. Rheumatoid arthritis (RA) is a chronic inflam-matory disorder characterked by hyperplasia of the

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