Aural barotrauma is a damage of the ear resulting from a pressure difference between middle ear and atmospheric environment. In order to investigate the pathogenesis of this disease, author used the hypobaric chamber flight which simulates the pressure variations of atmospheric environments in actual aircraft flights. Eighty six humans and six guinea pigs were exposed to changes in atmospheric pressure separately and the following results were obtained. 1) After the flight, 13(7.6%) among 172 ears showed abnormal findings. 11(12.8%) of 86 subjects complained of barotalgia and 9(10.5%) of them had barotitis media. 2) The incidence rate of barotrauma in the group suffering from upper respiratory infection or severe chronic rhinnitis before the flight were not different significantly from control group(p>0.05). 3) Valsalva test showed poor inflation in 3 subjects, and two of them had concurrent upper respiratory infections. Barotrauma was developed in one case with poor inflation having upper respiratory infection. 4) Tympanogram showed abnormal function in 10 ears, 9 with C type, and 1 with B type. Pure tone averages(bone conduction/air conduction) revealed 5/10 dB to 2/20 dB with mean air-bone gap of 8.5 dB. 5) The static compliance of the tympanic membrane showed no significant difference before and after the flight. The middle ear pressure measured by peak pressure of the tympanogram was lowered by 33.08±8.68 daPa after the flight(p<0.05). 6) Six guinea pigs were exposed to 37,000 feet altitude and returned to the sea level of a atmosphere. After the flight, all animals showed histopathologic findings of barotitis media and the most prominent changes were found in the immediate sacrificed animals. 7) The major histopathologic findings were congestions in the tympanic membrane, vascular engorgement, edema and hemorrhage in mucoperiosteum of the middle ear.