The respiratory cilia of nine patients with cystic fibrosis were examined by electron microscopy. In contrast to patients with "immotile cilia syndrome," the cilia from the patients with cystic fibrosis contained dynein arms and radial spokes. A low percentage of abnormal cilia were detected in all nine patients, but, except for the occurrence of rippled cilia in these patients, the alterations were similar both in morphologic terms and incidence to alterations in a control group of patients with chronic bronchitis. Lesions included compound cilia, excess cytoplasmic matrix, and an abnormal number or arrangement of microtubular doublets. Patients suffering from cystic fibrosis do not exhibit ultrastructural ciliary alterations characteristic of immotile cilia syndrome.