Adjuvant-induced arthritis (AIA) can be passively transferred in Dark Agouti (DA) rats by spleen and lymph node cells after culture with Concanavalin A (Con A). A model not requiringin vitroCon A expansion and activation would be important in investigations of anti-rheumatic drugs in AIA. A new model using irradiated recipients fills this need. Donor DA rats treated with 0.1 ml complete Freund's adjuvant (CFA) containing 7.5 mgM. butyricum/ml were sacrificed 11 days after CFA injection, donor spleen cells harvested, and donor spleen cells injected intravenously into recipient DA rats previously irradiated with 5 Gy. Recipient rats developed arthritis 4-14 days after spleen cell transfer. This model can now be used to further define the effects of anti-rheumatic drugs in the passive transfer of AIA by eliminating the need for thein vitroCon A-induced expansion and/or activation of donor cells.