Human anterior subcapsular cataracts were examined by immunocytochemistry to investigate which types of collagen constitutes the subcapsular fibrous matrix. Types I, III, and IV collagen were shown to be immunologically positive by both light and electron microscopy. In light microscopy, types I and III collagen were stained diffusely whereas type IV collagen was stained in a streaky pattern in the opacities. The lens capsules were stained with antibody to type IV collagen, although the staining patterns were not homogeneous; the inner layers of the capsules were labeled more strongly than the outer layers. Neither type I nor III collagen was detected in the capsules. In electron microscopy, collagen fibrils were labeled with the antibodies to both type I and type III collagen. The lens capsules and multilamellae of the basement membranes in the opacities were labeled with the antibody to type IV collagen.