The neonatal rat, which has an immature retinal vasculature at the time of birth, is a potential animal model for retinopathy of prematurity since it has an established spindle cell retinal vasoformation pattern similar to that seen in the human. To determine if proliferative oxygen-induced retinopathy can be produced in the rat, 40 newborn rat pups were exposed from birth either to air for 25 days or to an 80% oxygen environment for 10 days, followed by 15 days in air. Extraretinal neovascularization was observed in 80% (16/20) of the rat pups exposed to hyperoxia (p less than 0.001) with a bilaterality of 87.5% (14/16). Mild to moderate vitreous hemorrhage was seen in only three eyes. Mesenchymal shunt or ridge formation was not demonstrated, nor was retinal detachment.