The transgenic mouse strain Mpv17 develops severe morphological degeneration of the inner ear and nephrotic syndrome at a young age (Meyer zum Gottesberge et al., 1996; Weiher et al., 1990). The audiograms (1-32 kHz) of Mpv17-negative mice were determined from auditory brain stem responses in young (2 months) and old (7 months) animals. Audiograms of age-matched wild-type mice with the same genetic background, but wild-type at the Mpv17 locus, were also determined. Furthermore, young Mpv17-negative mice that carried a human Mpv17 homologue gene were studied. NMRI mice served as a reference for normal hearing. Mpv17-negative mice suffer from severe sensorineural hearing loss as early as 2 months after birth. In the old Mpv17-negative mice no responses could be elicited at all. The 2 month old wild-type mice had normal audiograms, at 7 months only high threshold responses were seen. The poor audiograms of the Mpv17-negative mice are assumed to be the functional correlate of the morphological degeneration of the cochlea described earlier (Meyer zum Gottesberge et al., 1996). The finding that 2 out of 4 Mpv17-negative mice with the human Mpv17 gene had normal audiograms, shows that the gene inactivation can be functionally compensated by the human Mpv17 gene product.