It has recently been shown that patients with Kartagener's triad and also some subjects with similar symptoms, but without situs inversus, have a congenital abnormality of cilia as an explanation for their chronic airway symptoms; this disease has been named "the immotile-cilia syndrome" or more correctly "primary ciliary dyskinesia". Studying 27 such patients, we have found daily nose blowings since birth, chronic-recurrent sinusitis, and chronic secretory otitis media highly characteristic features. The frequency of common colds was not increased, and most patients did not suffer from repeated episodes of acute purulent otitis media. The number of ciliated cells with immotile cilia was increased, but only a single patient had completely immotile cilia; also the degree of asynchrony within the single ciliated cell was increased. Electron microscopy showed a decreased number of dynein arms in some patients, and abnormal arrangement of microtubules in others. Some patients, however, had normal ultrastructure, and this appeared to be associated with a hyperfrequent beating pattern. At least three subgroups of patients with primary ciliary dyskinesia can be delineated based on the motility-ultrastructure studies. Bacterial infection tends to reduce the number of ciliated cells with motile cilia, and viral infection (common cold) gives a very marked and long-lasting reduction in the number of ciliated cells. This may account for some otherwise unexplainable subchronic symptoms from nose and throat.