Tracheobronchial clearance was measured by a radioaerosol technique in 12 patients with bronchiectasis, seven patients with chronic obstructive lung disease expectorating mucoid sputum daily (group X), eight patients with chronic obstructive lung disease but negligible sputum expectoration (group Y), and 10 healthy subjects. The patients with bronchiectasis all expectorated purulent sputum daily (mean wet weight 47 g/day), had reduced forced expiratory volume in one second (FEV1) (mean 47.5% predicted), and were unable to avoid coughing during the six hour observation period. None of the patients with bronchiectasis or the healthy subjects were current smokers. There were five current smokers in group X and six in group Y. The mean FEV1 in group X was 41% predicted and in group Y 52% predicted, both values similar to that of the patients with bronchiectasis. Tracheobronchial clearance in the first six hours after inhalation of radioaerosol was significantly (p less than 0.01) slower in patients with bronchiectasis than in matched healthy subjects despite more proximal deposition of radioaerosol (p = 0.01) and more coughing (p less than 0.01) in the former. Tracheobronchial clearance in patients with bronchiectasis was impaired to a similar degree to that in patients with chronic obstructive lung disease but no bronchiectasis.