Mucociliary transport in the tracheobronchial tract was studies in 2 subjects by having them inhale a radioactively tagged test aerosol and by taking external measurements of the radioacitivity in the lungs for 2 hours. Both subjects had living, yet immotile seprmatozoa; the sperm tails lacked normal dynein arms, which are essential for the bending movements of sperm tails as well as of other cilia. The subjects were classified as suffering from Kartagener's syndrome (situs inversus, chronic sinusitis, and bronchiectasis) and were shown to have an extremely slow, probably absent transport. The results of the study were in agreement with a recent hypothesis explaining Kartagener's syndrome as due to a genetic lack of dynein arms. An estimate of the importance of mucociliary transport as a protective mechanism of the lung may be possible by examining patients suffering from Kartagener's syndrome.