We studied the ultrastructure and function of nasal cilia from non-atopic and atopic non-smokers, smokers, patients with chronic rhinitis and cystic fibrosis, and compared these to cilia from patients with primary ciliary dyskinesia (PCD). Atypical cilia were found in normal subjects and patients with a variety of chronic respiratory tract diseases, but the proportion was small (less than 5%). Ciliary wave form, beat frequency, and mucociliary transport were normal. In patients with PCD, the proportion of atypical cilia and ultrastructural abnormalities was significantly greater than normal subjects and patients without PCD p less than 0.0001. Beat frequency was reduced, ciliary wave form was grossly abnormal, and mucociliary transport was virtually absent. These findings suggest that ciliary ultrastructural abnormalities are related to altered ciliary function and have aetiological relevance in the generalized chronic respiratory tract disease of PCD.