Guinea pigs were passively sensitized by sera containing antidinitrophenyl reaginic antibody and specifically challenged by dinitrophenyl-bovine serum albumin injected through the stylomastoid foramen. Nystagmus, head deviation, negative summating potentials on electrocochleography, and an increase of threshold and wave I peak latency on auditory brain stem response testing were observed after local challenge. These physiologic changes were reversible and resolved within several days. We also used Tranilast before the specific challenge. It is a blocking agent of chemical mediator release from mast cells. Negative summating potentials and head deviation were not observed after the use of this agent. In the animals that showed physiologic changes, we observed endolymphatic hydrops, mast cell degranulation, and eosinophil infiltration histologically in the challenged side of the inner ear. These results suggest that the physiologic and histologic changes provoked in the inner ear of the sensitized animals may have been induced by type I allergy.