Relationship of circulating immune complexes to some inner ear disorders has been suggested recently. Thus, bovine serum albumin (BSA) nephritis, a model of chronic serum sickness, was made and morphological, immunological studies of cochlea were performed using light microscopy, transmission electron microscopy and immunofluorescent antibody methods. Group 1 consisted of animal sensitized with daily BSA injections for 90 days; in group 2, BSA was administered for 70 days, daily, and after a three-weeks interval, injections were continued for another 21 days; group 3 consisted of animals sensitized with daily BSA injections for 100 days followed by BSA injection into the facial nerve via the stylo-mastoid foramen. The animals (group 3) were sacrificed on day 1 and 4 following facial nerve sensitization for examination of cochlear morphological changes. No morphological changes were observed (group 1). Protrusion of marginal cells into endolymphatic space was seen, because of swelling of endoplasmic reticulum of the cells of stria vascularis's (group 2). Slight hydrops was present mainly in the basal turn (group 3). No IgG deposits were found in all groups. It appears that the changes in group 2 were caused by rather chronic nephritis than immune reaction. We conclude that damage induced in the cochlea is negligible compared to the extensive lesions observed in the kidney in chronic serum sickness.