Laminin is a basement membrane glycoprotein, widely distributed in body tissues. It has been found on capillary basement membranes in both developing and adult retinal vessels. Oxygen-induced retinopathy was produced in kittens and mice by exposing them to a high oxygen environment during the newborn period. When the animals developed a proliferative retinopathy after a period of survival in room air, they were sacrificed and the eyes enucleated and embedded in paraffin wax. Cross-sections were cut and de-waxed. After preliminary digestion with pepsin, we used a fluorescein isothiocyanate (FITC)-labelled double antibody technique to identify laminin-like immunoreactivity (LLIR). LLIR was found on both intravitreal and intraretinal new vessels in the kitten and mouse, indicating that it is probably secreted by endothelial cells during the formation of pathological new vessels.