Airway inflammation particularly with eosinophil infiltration is an almost invariant feature of asthma, though it may not be exclusive to asthma. BHR and atopy are common phenomena in asthmatics but not invariably so. Allergen-induced late asthmatic responses can increase non-specific hyperresponsiveness and bronchial responsiveness in turn is, at least from some studies, correlated with the degree of airway inflammation. Atopy is a major risk factor for the development of asthma and its persistence from childhood into adulthood. Airway inflammation occurs very early in the natural history of asthma. No therapeutic intervention in established asthma has been shown to achieve a cure or even modify the natural history of the disease. Therefore, further studies are urgently required to identify whether strategies of early intervention to prevent the development of airway inflammation will modify the natural history of the disease.