The absorption of gas from the middle ear--mastoid air cell system causes an average pressure decrease of 5 cm water per hour. Interference with the normal opening of the Eustachian tube causes increased negative pressure build-up, which stops gas absorption from the middle ear. High carbon dioxide tension is associated with metaplastic changes of mucosal stem cells into mucus producing cells. Ventilation of the middle ear is necessary for removal of the negative pressure as well as of the excess carbon dioxide. The problems associated with longterm ventilation tubes are reviewed, and some future prospects of permanent ventilation tubes are discussed.