Mutant animals with a particular type of cochlear pathology are an excellent model for studying the functional role of various cells of the cochlea. In homozygous WV/WV mutant mice we found a selective loss of outer hair cells as a constant defect with no progressive degeneration of the organ of Corti. The mice were followed throughout their lives and exhibited auditory brainstem responses that were elevated to about 50 dB SPL as compared to normal control animals. Sequential temporal bone studies showed that there was a selective loss of outer hair cells throughout the entire cochlea as seen in surface preparations. The inner hair cells were present in normal numbers and appeared to be essentially normal.