The presence of intermediate filaments in the inner ear of the newborn mouse was analyzed with immunofluorescence techniques using antibodies against the five classes of intermediate filaments: cytokeratins, vimentin, desmin, neurofilaments and glial fibrillary acid protein (GFA). Neurofilaments were found in all nerve fibers from the ganglion cell to the hair cell. In the vestibular ganglion two subpopulations of ganglion cells were identified: a minor part staining intensively with neurofilament and the major part of cells lacking this immunofluorescence. Vimentin occurred in a number of supporting structures in the membranous labyrinth, but not in vestibular or cochlear ganglion cells. Cytokeratins, desmin or GFA were not identified in the inner ear.