The ultrastructure of the mucosa of the eustachian tube was studied in four temporal bones showing tympanosclerosis, cholesteatoma, otitic meningitis and a grafted tympanic membrane (tympanoplasty). The mucosa of tube was abnormal in the four cases confirming the relationship between the state of the eustachian tube and the inflammatory process in the middle ear. The observed abnormalities included: ciliary loss, abnormal ciliary morphology and motility, oedema of the microvilli, hyperplasia of the goblet cells and the seromucinous acini, desquamation of the non-ciliated cells and appearance of mast cells in the lamina propria of the tube. Ciliary changes were the most frequent abnormalities and the morphological changes, in general, were fewest in the case of healed tympanoplasty. The pathophysiology of the morphological changes was discussed and correlated with the disease in the middle ear.