Resumo: The epithelial layer of the middle ear, a modified respiratory epithefum, lias an important role in the defense system; under inflamrnatory or pathological conditions this mucosa may undergo some protective changes. Mucosal specimens of the middle ear from patients who had chronic otitis media were studied and compared with specimens of normal middle ear using SEM. The epithelia were usually thick and the surface structure varied depending upon the place the biopsy was taken. Moreover, the structure was not uniforin even in the same biopsy; areas with great proliferation of secretory cells, other areas with high population of ciliated.cefs and areas with loss of superficial layer were observed. There were less ciliated cells than we expected. They were not homogeneously distributed, except for the Eustachian tube region. Most of tiús ciliated cells were morphologicaly normal, however a few isolated atrophic ones were also found. Cholesteatoma cases showed squamous epithelia with desquamating flat keratinized cells.