Dysfunction of the eustachian tube has been considered as a important factor in the development and course of the middle ear diseases and in the result of tympanoplasty. In traumatic perforation, Miller reported that all ears equilibrated -250mmH₂O to 0, but McCurdy reported that 29% of these patients showed residual pressure of -150~-200mmH₂O. The authors measured the eustachian tube function of 110 ears with central tympanic perforation due to chronic otitis media and 23 ears with traumatic tympanic membrane perforation by using acoustic impedance bridge. The results were as follows : 1) Among 110 ears with central tympanic membrane perforation due to chronic otitis media, good function was noted in 10.0% by negative pressure equalization test and in 40.9% by positive pressure equalization test. The percentage of good function was higher by positive pressure equalization test than by negative pressure equalization test (P<0.05). 2) Among 62 wet ears, good function was noted in 9.7% by negative pressure equalization test and 30.6% by positive pressure equalization test. The percentage of good function was higher by positive pressure equalization test than by negative pressure equalization test (P<0.05). 3) Among 48 dry ears, good function was noted in 10.4% by negative pressure equalization test and in 54.2% by positive pressure equalization test. The percentage of good function was higher by positive pressure equalization test than by negative pressure equalization test (P<0.05). 4) In negative pressure equalization test of 62 wet ears and 48 dry ears, no difference of eustachian tube function was noted between dry and wet ears (P>0.05). 5) In positive pressure equalization test of 62 wet ears and 48 dry ears, no difference of eustachian tube function was noted between dry and wet ears (P>0.05). 6) Among 23 ears with traumatic tympanic membrane perforation, good function was noted in 30.4% by negative pressure equalization test and in 82.6% by positive pressure equalization test. The percentage of good function was higher by positive pressure equalization test than negative pressure equalization test (P<0.05). 7) In negative pressure equalization test of 48 dry ears and 23 traumatic perforations, good function was noted in 10.4% and 30.4% and poor function was noted in 56.3% and 13.1%. The percentage of good function was not different between dry ear and traumatic perforation (P>0.05) and the percentage of poor function was higher in dry ear than traumatic perforation (P<0.05). 8) In positive pressure equalization test of 48 dry ears and 23 traumatic perforations, good function was noted in 54.2% and 82.6% and poor function was noted in 31.2% and 0%. The percentage of good function was not different between dry ear and traumatic perforation (0>0.05) and the percentage of poor function was higher in dry ear than traumatic perforation (P<0.05).