Abstract
In the 1970s studies in humans showed that mucociliary transport in the tracheobronchial tract was affected by various agents and diseases. Perhaps the most important finding was that persons with chronic bronchitis usually had severely impaired tracheobronchial clearance. How should this impaired clearance be interpreted? Is it just a result of an inflammatory process in the airway mucosa with no or little importance for the pathogenesis of the lung disease? Or is the impaired clearance of importance for the development of airway obstruction?