Morpho-pathological features, observed by scanning electron microscopy, in guinea pigs with endolymphatic hydrops of 4-14 months included shortening of the hair cell tufts, loss of tufts, retraction of sensory hair cells away from the surrounding tissue and hair cell loss. After 22 months of hydrops, there was complete loss of hair cells with indifferentiation of the epithelium. The loss of ciliary tufts involved loss of both stereocilia and kinocilia identified as short stubs and holes respectively. Control macular epithelia showed no hair tuft loss although ampullae in control ears could show some loss