BACKGROUND: To evaluate airway responses and inflammation to antigen in Sprague-Dawley rat asthma model, we examined airway responses, serial histologic changes of the lung, and the relationship between airway responses and airway inflammation after antigen airway challenge. METHODS: Sprague-Dawley rats were sensitized with subcutaneous injection of 10 microgram ovalbumin(OA). Antigen airway challenges were done 14 ~16 days after sensitization and the sensitized rats were sacrificed 1h(AE), 6 ~8h(AL) and 1day(AD) after airway challenge, to examine the histologic changes of the lung. Airway responses were measured by body plethysmograph and recorded by enhanced pause(Penh) as an index of airway obstruction 6 ~8h after antigen challenges. Nonsensitized controls(10 rats) were also challenged with antigen and sacrificed 1 day later. Histopathologic examination of two trachea, large bronchi, small bronchi, and vessels was performed to evaluate the severity of inflammation and eosinophilic infiltration with H