In order to investigate the effects of accumulation and activation of eosinophils on the airway responsiveness we developed an animal model of eosinophilic airway inflammation by administration of polymyxin B. Bronchoalveolar lavage confirmed the presence of significantly increased numbers of eosinophils in polymyxin B-treated guinea pigs compared with that in saline-treated guinea pigs. Contrary to our expectation, no significant increase in airway responsiveness was obtained in polymyxin B-treated group. The results also showed that both intratracheal instillation and inhalation of FMLP to polymyxin B-treated guinea pigs enhance the airway responsiveness to intravenous 5-HT. The indice of eosinophil activation, EPO activity after the FMLP administration in polymyxin B-treated guinea pigs was significant increased. It suggested that accumulated eosinophils be highly activated. The results indicate that eosinophil accumulation does not necessarily cause AHR and accumulated eosinophil activation plays an important role in the development of AHR. Accumulated eosinophil activation would be one of the trigger for asthma attack.