In the present work, vessels casts in the inner ear of the rat and guinea pig, prepared by casting method using Mercox resin, were subjected to scanning electron microscopic examination and following results were obtained: In adult guinea pig, numerous capillary nets were found in the following parts: stria vascularis, spiral ligament, spiral prominence, Corti's organ, spiral ganglion, plexus cochlearis, semicircular ampulla, saccule, utricle, and endolymphatic sac. These were consistent with functionally and morophologically important areas in the inner ear. In the central side of the area with capillary nets, arterioles were found to run throughout, like a complex coil, and peripheral capillary diameter was found to be unchanged in an experiment in which the injection pressure was altered, thus autoregulation of blood flow into these important areas is assumed. Vessels in the planum semilunatum were found to form a specific loop-shaped route, where secretion and reabsorption of endolymph is thought to occur. After kanamycin injection into the tympanic cavity, stenosis was observed in capillary nets in the cochlear lateral wall. In guinea pigs on the 30th day of fetal life, the main stem of the inner ear vessel had already formed; however, the peripheral capillary nets were as yet immature in form and vessel density was low.