Endolymphatic hydrops was induced in guinea pigs by immunizing them with native bovine type II collagen. Histopathologic changes consisted of moderate extension of the Reissner's membrane, spiral ganglion degeneration, atrophied organ of Corti, and mild atrophy of the surface epithelium in the endolymphatic duct. These findings suggest that an immune response directed against type II collagen—a type of collagen found in the membranous labyrinth, subepithelial layer of the endolymphatic duct, spiral ligament, and enchondral layer of the otic capsule—may induce endolymphatic hydrops.