Following optimized fixation and specimen handling, the endolymphatic duct was investigated by transmission and scanning electron microscopy. Tubular microfibrils, 10-12 nm thick and of indefinite length, occupied the subepithelial compartment abundantly and seemed to insert into the basal lamina of the epithelial cells of the duct and to merge with the bony wall of vestibular aqueduct thus forming a suspensory ligament of the endolymphatic duct. This ligament is suggested to protect the endolymphtaic duct from collapsing and to play a role in the mechanical protection of the vestibular apparatus from sudden increases in intracranial pressure. The capillaries and the aqueductal vein were located in intimate relationship to the epithelial cells. Both types of vessels were provided with fenestrations of the endothelial cells, supporting the proposal that the endolymphatic duct may be involved in the resorption of endolymph.