By injection of guinea pig cochlea emulsified with Freund's adjuvant, it was possible to induce in the majority of guinea pigs the acoustical and histological disturbances which were interpreted as an isoimmunization to cochlea tissue, although the detection of anticochlea antibody failed. No positive reaction occurred when adjuvant alone was injected. The main histological changes were found in the spiral ganglion and stria vascularis. In some animals, hemorrhage in the scala tympani and disintegration of the organ of Corti were observed. These changes generally corresponded to the acoustical threshold shifts. Thus there may be possibilities that the inner ear disease of one ear could affect the opposite ear as the result of an autoimmune reaction.