Hearing acuity and inner ear disorders of MRL/lpr mice, bred for the study of autoimmune disease, were examined in comparison to those of BALB/c mice. The auditory brain stem response threshold of 20-week-old MRL/lpr mice was significantly higher than that of BALB/c mice of the same age (p < .01). The pathologic changes of 20-week-old MRL/lpr mice were characterized by the degeneration of intermediate cells, widened intercellular spaces, and immunoglobulin G deposition on the basement membrane of strial blood vessels as well as in the basal infolding of strial marginal cells, which were absent in BALB/c mice. That there were no other evident pathologic findings in the cochlea or middle ear suggests that these changes in the stria vascularis seemed to be responsible for the sensorineural hearing loss of this mouse. The MRL/lpr mouse was thought to be a good experimental model to study the spontaneous sensorineural hearing loss caused by an immune reaction.