In this study, nasal mucociliary clearance is investigated in patients with primary ciliary dyskinesia, patients with other respiratory tract infections and healthy persons. Mucociliary clearance is established with a drop of albumen labelled with ^99m-Tc. From this study it appears that measurement of mucociliary clearance in the nose can serve as a reliable screening method. If a patient with respiratory tract infections shows a normal mucociliary clearance rate there is no primary ciliary dyskinesia, and a biopsy of ciliated epithelium is not necessary. If, after repeated examinations, a normal clearance rate cannot be demonstrated, a biopsy of ciliated epithelium should be taken for studying ciliary activity and ciliary ultrastructure