The distribution of type IV collagen (C-IV) and laminin, which are important components of the basement membrane (BM), was studied immunohistochemically in the inner ear of healthy Hartley guinea pigs. Antibodies against C-IV and laminin were used in this study. The distribution of C-IV in the inner ear was almost the same as that of laminin, but the extent of staining for laminin was less than that for C-IV in some sites. The sites of the inner ear in which these components were most densely localized were the areas surrounding the spiral ganglion cells and nerve fibers, the capillary vessels in the stria vascularis and the spiral prominence, and an area directly beneath the epithelium of the endolymphatic sac. Type IV collagen and laminin were also localized around the other vascular BM and the epithelial BM in the inner ear, but the tectorial membrane, the cupula of the crista ampulla, and the sensory epithelium did not take up stain. These results suggest that the vascular BM of the stria vascularis and spiral prominence, as well as the epithelial BM of the endolymphatic sac, may play an important role in fluid transport, and that the perineural BM of the inner ear might play an important role in the functional maintenance of the optimal environment of the inner ear nervous system.