Nitrogen dioxide has been shown to have a deleterious effect on the structure and function of respiratory cilia. This study focuses on both the alterations of cilia morphology, and the ciliated cell response induced by nitrogen dioxide, in order to determine the mechanism(s) leading to ciliary dysfunction. Ciliated cells of the respiratory airways of hamsters, exposed to 30 ppm nitrogen dioxide for 5 months, 7 days/week, 22 hours/day, were examined ultrastructurally using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) of thin sections, freeze-fracture replicas, and thin sections of tissues treated with cationized ferritin. SEM and TEM preparations appeared to show a generalized reduction in number and length of cilia. It was common to see basal bodies with no ciliary shaft and many cilia at different stages of growth. It was also apparent that the cilia were most fragile just below the ciliary necklaces. After breakage, the plasma membranes of the remaining ciliary stubs covered the exposed basal bodies. During the early stages of ciliary regeneration, freeze fracture replicas showed the emergence of membrane particles which appeared to correlate with cationized ferritin binding sites. As the cilia increased in length, the particles assembled into a necklace-like arrangement, varying in ring number and particle distribution as compared to the 5 to 7 well organized rings observed in controls. In corresponding thin sections, cationized ferritin appeared bound to sites in the region of the ciliary necklace particles. As the cilia developed further, the cationic ferritin binding at these sites diminished. This data suggests that nitrogen dioxide had an affect on the plasma membranes of ciliated cells. One of the major sites affected by the nitrogen dioxide was the ciliary necklace region. Exposure to nitrogen dioxide appeared to lead to increased ciliary fragility, stunted ciliary growth, and loss of ciliary motility. The rings of ciliary necklace particles exhibited an 8.4 degrees +/- 1.3 degree angle of pitch to a perpendicular through the longitudinal axis of the cilium. The measurable pitch and the identification of ciliary necklace "free ends" proximally and distally lead us to hypothesize that the particle arrangement of the ciliary necklace is that of a single spiral and not separate rings.