The Eustachian tube dysfunction has been considered as one of the most important factors in the pathogenesis of middle ear diseases and the quantitative assessment of Eustachian tube function has been known to be helpful and important in the diagnosis, treatment, prognosis and prevention of the disease. There have been two opposite theories on the etiology of the hypocellularity : The one theory, according to Diamant⁴⁾ et al., is that the hypocellularity of mastoid is genetically determined and makes middle ear more susceptible to infection, and the other, held by Tumarkin²⁷⁾, is that the hypocellularity results from impaired middle ear ventilation due to mechanical effect of persistent Eustachian tube obstruction. The relationship between the Eustachian tube function and degree of mastoid aeration of 102 ears with central tympanic membrane preforation of 82 patients was analyzed after obtaining them respectively by using valsalva maneuver and inflation-deflation test, and by measuring the pneumatized matoid area by planimetry on Law's view of temporal bone. The results obtained were as follows : In inflation test of total 102 ears 37.3% showed residual pressure of 0~19mm H₂O, 22.5% showed 20~199mmH₂O, and 40.2% showed no change of the pressure given. In deflation test of total 102 ears 19.5% reached residual pressure of 0~-19mmH₂O, 31.4% reached -20~-199mmH₂O, and 49.1% showed no pressure change. The mean value of the pneumatized mastoid area of 95 normal control ears was 9.8cm² and that of chronic otitis media was 2.09cm². Among 29 dry ears with normal tubal function in inflation test of total 56 dry ears, mastoid air cell area was under 3cm² in 54.5%, between 3~6cm² in 37.5%, and over 6cm² in 71.4%. Among 15 dry ears with normal tubal function in deflation test of total 56 dry ears, mastoid air cell area was under 3cm² in 18.2%, between 3~6cm² in 35.7% and over 6cm² 57.1%.