In order to clarify the possibility of pharmacokinetic interaction between quinolone and fenbufen, the plasma concentration-time profiles and serum protein binding of enoxacin, fenbufen and its active metabolite, felbinac, were investigated in rats. The rats were administered an intravenous dose of enoxacin (5 mg/kg) and fenbufen (10 mg/kg) alone or concomitantly. Coadministration with fenbufen tended to prolong the plasma elimination half-life of enoxacin by about 20%, whereas it showed no effect on the area under plasma concentration-time curve, total body clearance or distribution volume of enoxacin. The extent of enoxacin binding to rat serum tended to be slightly reduced by fenbufen in vivo and in vitro. Plasma concentration-time curves, pharmacokinetic parameters and serum protein binding of fenbufen and felbinac were not affected at all by the coadministration with enoxacin. These aspects suggest that there may be only a minor possibility of the pharmacokinetic interaction between enoxacin and fenbufen.