The effects of the middle ear pressure regulation are important to the understanding of normal and pathological middle ear function. The physiological middle ear pressure depends on the functional states of Eustachian tube, the middle ear volume, the mechanical properties of the ear drum system and the volume changes of the mucosa of the middle ear. Most research on the gas turnover has been based on the presumption that oxygen is continuously being absorbed through the mucosal lining of the middle ear cavity. But, recent studies suggest that gas exchange may affect the middle ear pressure (MEP). A group consisting of 17 persons with both healthy ear served as a study population. The authors measured middle ear pressure changes between daytime and sleeping. And one person with normal pulmonary function used for middle ear pressure changes to hypoventilation and hyperventilation. MEP was measured by Impedance Audiometer (GSI 28 Auto Tymp. Model). The results were as follows ; 1) During the sleeping, MEP increased in all except 2 cases. 2) In hypoventilation, MEP increased every 5 minutes. 3) In hyperventilation, MEP decreased every 10 minutes.