In mucoviscidosis, even the clinically and histologically often normal appearing nasal mucosa exhibits characteristic changes with the electron microscope. The epithelial cells show intra- and extracellular edema, the cilia membrane damage. The highly viscous mucous blanket and the frequent lamination of the basement membrane of the capillaries can be explained by a disturbance in mucopolysaccharide and glycoprotein metabolism respectively. The functional disorder of the goblet cells and the nasal glands manifests itself with signs of increased activity, but without definite degenerative changes. The course of the pathologic mucous formation on the cells appears morphologically normal so that a disturbance of membrane transport or in the dilution of the secretions must be assumed. The endonasal polyps differ from allergic polyps by the absence of eosinophilic infiltration.