Two and 4 weeks after experimental tubal occlusion in germ-free rats the goblet cell density in the middle ear was increased, compared with the normal contralateral side, indicating that transformation of epithelial cells to secretory cells can occur without infection. Other histopathological changes such as vasodilatation, oedema, round cell infiltration, fluid uptake of epithelial cells (which were thereby distended), hyperplasia of the epithelial cells, formation of intra-epithelial glands and some few subepithelial glands, are described. The finding may indicate that negative middle ear pressure and fluid uptake into the cells damage the epithelium, and the succeeding processes may be regarded as reparative processes following the epithelial damage.