Inner ear barotrauma was observed by compressing or decompressing guinea pigs. The barotrauma in compression was greatly influenced by auditory tube function, and, in the animals deprived of this function, we could observe far more severe damage of inner ear hair cells and far more frequent round window rupture than in animals not thus deprived. Barotrauma in decompression was brought about in guinea pigs not deprived of auditory tube function with a decompression speed of 0.1 kg/cm2/sec, which is so severe that even a healthy auditory tube could not endure it. It can be said that the middle and inner ear are more apt to be damaged in decompression than in compression.