It is known that radiation therapy of the head and neck causes otitis media with effusion. Otitis media with effusion was induced in guinea pigs by cobalt-60 irradiation. Twenty guinea pigs with intact drum and normal Preyer reflex were used. We conducted, two experiments as follows:
1) The animals were irradiated with doses of 2, 000 rad, 4, 000 rad, and 6, 000 rad. They were sacrificed seven days after the irradiation.
2) The animals were irradiated with doses of 4, 000 rad and sacrificed one day, three days, seven days, and fourteen days after the irradiation.
Vascular permeability of the middle ear mucosa was observed by Majno's vascular labelling technique. Pathological change of the middle ear was examined under the light microscope. Vascular permeability increased in three days after 4, 000 rad irradiation and small vessels were labelled with carbon particles. Seven days after irradiation, carbon labelling of small vessels was more extensive and extravascular blackening was present in the adjacent tissues. Edematous change of the middle ear mucosa and metaplasia of the epithelial cells were also observed. New bone formation of the tympanic bulla was increased by repeated irradiations.