Mucosal oedema and airway hyperreactivity are common features of asthma, in which they seem to share a common pathogenesis, i.e. airway inflammation. The relationship between oedema and hyperreactivity has not yet been properly investigated. Some speculations are advanced, based on the available experimental evidence. Mucosal oedema may amplify bronchial responsiveness by increasing epithelial permeability, by altering airway mechanics, or by stimulating neural pathways. On the other hand, bronchoconstriction may contribute to oedema by increasing hydrostatic pressure in postcapillary venules.