By using well-defined monoclonal antibodies, the distribution of synaptophysin and the glycoprotein Egp-34, the first of its kind, was analyzed immunohistochemically in the fetal and the adult human inner ear. In fetal labyrinths, a distinct immunoreactivity for synaptophysin occurred in the apical region of both outer and inner hair cells as well as in nerve terminals adjacent to both cochlear and vestibular hair cells. In adult hair cells, immunoreactivity was found throughout the cytoplasm. Synaptophysin may act as an important calcium binding protein in the sensory transduction of hair cells. A selective expression of Egp-34 was found in the area of marginal and intermediate cell infoldings in the stria vascularis. A similar localization pattern was found for a number of membrane transport enzymes. The glycoprotein Egp-34 is probably of importance for the active mechanisms regulating the homeostasis of endolymph.