Two weeks following direct antigen (KLH) secondary challenge of the endolymphatic sac (e. sac), caloric responses were significantly suppressed in the KLH challenged ears as compared to the unchallenged ears. Perilymph antibody levels to KLH were found to be significantly elevated in the KLH challenged ears. The local accumulation of plasma cells and lymphocytes was seen in the perisaccular space and the e. sac lumen. Haemorrhage in the vestibule, vacuolization of hair cells in both of the macula and the lateral crista and endolympahtic hydrops in both of the saccule and the cochlea were seen.