Observations of freeze-fracture preparations of human nasal epithelium have provided a unique perspective of the spatial distribution of epithelial cell cilia unattainable by more conventional ultrastructural techniques. The initial stages of ciliogenesis were characterized ultrastructurally in these preparations by differentiation of the lumenal aspect of the epithelial cell membrane prior to the emergence and maturation of new cilia. Morphometric analyses of the resultant electron micrographs indicate that the development of an optimal ciliary population during differentiation of ciliated cells may be integral to the adequate functioning of respiratory mucociliary mechanisms. The frequency with which such ciliogenic structures are observed indicates that ciliogenesis is a common feature of the nasal epithelium and suggests that epithelial cell turnover in the nasal cavities is relatively rapid.