In the normal rat retina ganglion cell axons are not myelinated until they enter the optic nerve. After a lesion to the retina made via the sclera and choroid, Schwann cells invade the retina and myelinate ganglion cell axons. The lesion-induced myelin formation is most conspicuous in animals operated between the day of birth and 20 days of age. A lesion to the retina made from the vitread surface does not produce Schwann cell invasion. We suggest that the Schwann cells migrate into the retina from extraocular structures via the sclera. These observations provide a valuable system for the study of interactions between CNS axons and Schwann cells.