The neurosensory epithelium of the cochlear duct becomes the organ of Corti, a region specialized for sound detection. Neurotrophin-3 (NT-3) is essential for completing the development of the spiral ganglion and thus the afferent innervation of the sensory cells in the organ of Corti (Ernfors ' et al'., 1995). Colvin ('et al'., 1996) demonstrated that 'FGFR3' was pivotal for normal organ of Corti development. Using CD-1 mice, we have previously shown that localization of mRNA for fibroblast growth factor receptor 3 (FGFR3) was limited to a discreet region of the neonate murine organ of Corti. The aim of this study was to determine whether or not the presence of spiral ganglion cells and their afferent innervation to the sensory cells affects the expression of 'FGFR3' in the organ of Corti. For these studies, mice deficient in NT-3 were used because they have reduced afferent innervation to the organ of Corti (Ernfors ' et al'., 1995). 'In situ' hybridization, was used to compare 'FGFR3' mRNA localization between NT-3 deficient mice and wildtype mice at ages E19 and P0. Localization of 'FGFR3' appeared consistent in all genotypes. 'FGFR3' mRNA was localized to the precursors of outer hair cells and supporting cells in the organ of Corti. These results suggest that the neurosensory epithelium and the tunnel of Corti start to form even with sparse or abnormal routes of innervation to the hair cells, and always in the presence of cells that synthesize ' FGFR3' mRNA.