Different strains of mice provide a valuable research tool for studying both hereditary and acquired forms of deafness. The cd/1 strain has been found to demonstrate hereditary cochlear pathology. The characteristics of hearing loss in cd/1 mice have not previously been reported. In this investigation auditory thresholds were obtained by measuring evoked brain stem responses in subjects of three different ages: 3 weeks, 10 weeks and 6 months. The results were compared with thresholds obtained from CBA/Ca mice (which have normal hearing) and C57BL/6 mice (which are known to have a genetically determined pre-senile progressive cochlear hearing loss). A significant hearing loss was observed which progressed from high to low frequencies, and with age. Extensive degeneration was observed throughout the organ of Corti. cd/1 mice may provide a useful model for studying genetically determined deafness.