23 specimens with endonasal polyposis are examined scanning-electron-microscopically. There is a domination of kinocilia-free epithelium. The latter is bulging out in a dome-shaped manner, extensively loosened, showing transitional forms from cylindrical epithelium to more cube-like and finally squamous epithelium. The cylindrical epithelium is partly closely joined, showing ballon-like bulgings, cytoplasmatic protuberances, filled beaker cells with reduced or missing microvilly and partially granulating surface as well as emptying beaker cells with a thin microvilly edge. The covered surface shows partially normal lawn- and/or bundle-like, long and most parallel kinociliae, and short thin kinociliae in small bundles. All of them have a coordinated direction and a morphologically evident function-phase. In addition there is a network of kinociliae without function-phase and coordinated direction, which may or may not be covered by mucous, as well as damage and reproliferation of kinociliae. By reason of the morphological findings one can come to the conclusion that there is an extensive decrease in function of the mucociliar system in case of polyposis and as a consequence of this bacterial and viral infections might be favoured.