Temporal bones from four patients with capsular otosclerosis were examined by microdissection. Otoconia and abnormal crystalline deposits were studied by scanning electron microscopy and x-ray analytical methods. One patient showed more or less symmetrical invasion of the basilar membrane and osseous lamina by connective tissue from thickened endosteum adjacent to the larger anterior foci. In one ear sensorineural degeneration was circumscribed; in the other it was extensive and associated with cochleosaccular hydrops. Two other patients were deaf, with severe sensorineural degeneration; one had multiple active foci and evidence of cochleosaccular hydrops. In the fourth patient, who had small anterior foci, no specific inner ear pathology was found related to otosclerosis. In the hydropic labyrinths, apatite was present as abnormal deposits in the cochlear duct and as rigid crusts replacing the otoconia. Apparently these changes had been associated with abnormal labyrinthine fluid dynamics rather than with the otospongiotic process per se.