Morphological features of Reissner's membrane were investigated in 6 patients with age-related normal hearing (ARNH) and in 4 with sensorineural hearing loss (SNHL) stemming from various causes. The membrane consisted of an epithelium, a basement membrane and a mesothelium with melanocytes. There were two major forms of epithelial cells: flat and rounded. In all specimens, the rounded cells formed whorls, clusters, strands and bands. The bands were wider and the whorls larger in the basal turn and decreased gradually in size toward the apex. The number of melanocytes was 2-4 times higher in both the upper half of the basal turn and the lower half of the middle turn than in the rest of the turns. In specimens from patients with SNHL, whorls and clusters were both more numerous and larger, and the number of melanocytes was higher in the upper half of the middle turn and in the apical turn than that in the ARNH group. Ultrastructural examination of epithelial and mesothelial cells as well as of melanocytes showed more pronounced cellular degeneration in patients with SNHL than in those with ARNH. A possible correlation between structural alterations of Reissner's membrane and sensorineural degeneration is discussed.