In our present study we examined the pathology of the nasal mucociliary system after x-ray irradiation in an animal model namely the rabbit. A reduced ciliary activity was observed immediately after the irradiation and did not show any recovery during our observation. No ciliary activity was seen in the nasal mucosa 8 weeks after the irradiation. Morphologically, hypersecretion of goblet cells was observed immediately after irradiation. Cytoplasmic vacuolation and nuclear pyknosis of ciliated cells started after irradiation, and sloughing of ciliated cells was observed for up to 3 weeks. Epithelial metaplasia started from 4 weeks, and no cilia were seen in the nasal mucosa and the surface of the epithelium was covered with flat squamous cells. Our present study shows that x-ray irradiation has serious influence on the function and structure of the nasal mucociliary system and that recovery from degeneration due to x-ray irradiation cannot be expected within several weeks.