Using cuprolinic blue staining, we histochemically examined the ultrastructural localization of proteoglycans in the fibrous-type human posterior capsule opacification. This capsule opacification contained proteoglycans that showed positive staining with cuprolinic blue. Many cuprolinic-blue-positive filaments were present within the bundles of collagen fibrils, basal lamina-like material and basal lamina of proliferated lens epithelial cells. Pretreatment with enzymes and nitrous acid revealed that the collagen fibrils contained chondroitin sulfate and dermatan sulfate, whereas the basal lamina-like material and basal lamina of epithelial cells contained heparan sulfate. These results suggest that proteoglycans are one of the components in posterior capsule opacification.