Mucociliary function is governed by cilia, mucus, and their interaction. To play their role in mucociliary function, cilia must be present in large number. It has been reported that the ciliary area is reduced in acute and chronic inflammations of the upper respiratory mucosa. However, quantitative observations of the ciliary area in these conditions have not been reported. In this study, ciliary areas of the maxillary turbinate infected with the B strain of Newcastle disease virus (NDV) were quantified with a scanning electron microscope and an image analyzer. The epithelial surface occupied by cilia was calculated by an image analyzer. The ciliary area was expressed as a percentage of the total area examined. Ninety 21-day-old chickens were inoculated intranasally with NDV. The ciliary area and mucociliary transport time were examined periodically. The ciliary area was reduced about 50% on day 5 and then recovered gradually to normal by day 21. The ciliary area was reduced by increasing amounts of inoculated virus. A negative correlation was noted between histopathologic severity and ciliary area. The mucociliary transport time in the NDV infected nasal mucosa increased as the percentage of the ciliary area decreased. In this study, reduction of the area occupied by cilia caused deceleration of nasal mucociliary transport. Quantitative analysis of the ciliary area can clarify the role of cilia in mucociliary dysfunction.