The effect of flurbiprofen on the passive transfer of adjuvant-induced arthritis was studied to determine if flurbiprofen acted in the donor and/or recipient arms of this model. Groups of donor and recipient rats were treated with either placebo or flurbiprofen 4 mg/kg. Joint scores were markedly decreased in recipient rats treated with flurbiprofen irrespective of the whether donor animals were treated with placebo or flurbiprofen (p less than 0.01). There was also a moderate decrease in the ability of donor cells from rats treated with flurbiprofen to suppress the severity of arthritis (p less than 0.01); however, this effect was less marked than that seen in recipient animals. These data imply that flurbiprofen may act at multiple sites in adjuvant-induced arthritis, but the major site of action of flurbiprofen in this model is in the recipient animals.