Albino rats were maintained in 60% oxygen from birth through 14 days of age. Control rats were simultaneously maintained in room air. At the end of the exposure period some animals from both groups were prepared for electroretinography and, following this analysis, were sacrificed for histological scrutiny of retinal vasculature. The rest of the rats were removed to room air and allowed to remain for various periods of time before electroretinography and sacrifice. Some of the retinas from the latter group were analyzed for the presence of glial fibrillary acidic protein (GFAP) by immunocytochemistry. Oxygen exposed rats had a permanent reduction of the b-wave of the electroretinogram (ERG). The a-waves of the two groups were indistinguishable. Control rats showed GFAP reactivity in the retinal astrocytes at all times. The oxygen-treated rats showed positive GFAP-staining in astrocytes at all times and in Müller cells from 2 weeks post-treatment through 8 weeks post-treatment, the last time point. Immunoblot analysis confirmed that the anti-GFAP reacted with a protein having a molecular weight and solubility characteristics like those of GFAP. These results indicate that Müller cells produce GFAP in response to oxygen-rearing in newborn rats and that this production occurs in the absence of any detectable neuronal cell death.