The effect of increasing water content in inspired air on specific airway resistance in rats was assessed. The results showed that specific airway resistances were significantly related to the water content of inspired air, above 15.02 mg/m3, the duration of water content exposure and to the type of water nebulized. It is suggested that theincrease in specific airway resistance is composed of a local and neural element caused by accumulation of mucus or mucosal swelling and changes in the composition and consistency of the mucus lining layer, respectively.