Brn3c is a POU domain factor that is crucial for inner ear hair cell development. Targeted null Brn3c mutants have no mature hair cells [1,2]. Close examination has revealed that some 'immature' hair cells form in Brn3c null mutants and express cellular markers such as Myosin VI and VIIa, calretinin and parvalbumin [3]. Furthermore, these immature hair cells of Brn3c null mutants undergo apoptosis in neonates [3]. Consistent with an apparent absence of mature hair cells, initial work suggested that all vestibular and most spiral ganglion cells are lost by postnatal day 14 (P14; [1]). However, more detailed quantification by others [3] reported that at P4 about 77% of vestibular neurons and only 29% of spiral neurons are lost. It was suggested that there is possibly a complete loss in adults [3]. Other than these preliminary statements, no data exists concerning the detailed pattern of loss of innervation in Brn3c null mutants.