Twentyfour adults, aged 19-47 years, with congenitally nonfunctioning cilia were investigated by clinical examination, radiography, spirometry, and in most cases by tracheobronchial clearance measurements and ultrastructural examination of respiratory tract cilia and/or sperm tails. They all suffered from chronic bronchitis, rhinitis and sinusitis, and most of them had bronchiectasis and a history of otitis. Most had spirometrically overt obstructive lung disease and four radiological signs of emphysema. Clinical profile, lung function and mucociliary clearance data were compared to corresponding data from samples of patients with other obstructive lung diseases. These comparisons indicate that a long-standing impairment of mucociliary clearance is of pathogenetic importance in common chronic obstructive lung disease associated with chronic bronchitis, but not in emphysema associated with severe alpha 1-antitrypsin deficiency without chronic bronchitis, and not in asthma. In cystic fibrosis and in hypogammaglobulinemia an impaired clearance is not of primary pathogenetic significance but may contribute to the development of obstructive lung disease.