The role of mucociliary transport in man can be evaluated by studying persons with the recently recognised "immotile-cilia syndrome". Such persons have chronic or recurrent infections of the upper and lower airways and have ultrastructural defects of cilia and sperm tails. Men suffering from the syndrome usually are sterile and have immotile spermatozoa. About half of the subjects have complete situs inversus. Fourteen persons with the immotile-cilia syndrome have been studied here in an attempt to evaluate the role of an impaired mucociliary transport for the development of obstructive lung disease. Age range was 25-40 years; there were ten men and four women. Mucociliary transport in the lungs was extremely slow in all subjects. Spirometry demonstrated airway obstruction in nine subjects. Two of these subjects had radiological evidence of pulmonary emphysema. The results indicate that an absent mucociliary transport predisposes to the development of obstructive lung disease. Patients with classic chronic bronchitis have earlier been shown to have a severely impaired mucociliary transport. The present findings in subjects with primary ciliary immotility make it probable that this impaired mucociliary transport is of pathogenetic importance for development of the obstructive lung disease often found in patients with chronic bronchitis.