Three-dimensional analysis of 61 human endolymphatic ducts and sacs in ears with and without Meniere's disease. We used light microscopy and computerized graphic reconstruction techniques to examine the endolymphatic duct and sac in 20 pairs of bones from patients with Meniere's disease and 21 bones from controls. The diameters of the endolymphatic duct and the proximal portion of the vestibular aqueduct were significantly smaller in Meniere's disease ears than in controls. Graphic reconstructions showed the Meniere's sacs to be smaller and to have fewer tubular epithelial structures in the intraosseous portion than in the control ears. The median volume of the sac in the Meniere's disease side was substantially lower than in the contralateral ear. The width of the external aperture of the vestibular aqueduct was significantly smaller in Meniere's disease ears than in controls. These findings indicate that the size not only of the vestibular aqueduct but also of the sac is reduced in Meniere's disease. The results may suggest that the endolymphatic sac is pathologically changed in Meniere's disease and that a reduced resorptive capacity of a small endolymphatic sac could result in endolymphatic hydrops. 