The interrelationship of cilia and the directional disorder of the ciliary metachronal wave were analyzed using digital microscopic images. The degree of synchronization between ciliary beats was determined by the correlation. factor between two different spots. Principal axes of inertia were applied to find out the uniphase directions of beating cilia. The standard deviation of wave directions in a ROI was defined as a measure of ciliary wave disorder (CWD). The pooled mean of CWD was 22.9+/-8.73/spl deg/ in ROIs of 8 /spl mu/m/spl times/8 /spl mu/m and 25.4+/-6.46/spl deg/ in 32 /spl mu/m/spl times/24 /spl mu/m from the sphenoid sinus mucosa of 5 normal subjects. Our result shows that there is a considerable variation in metachronal wave directions of cilia beating on the epithelium.