Developing retinas from 13-18-day fetuses and 2-day neonatal Long-Evans rats transplanted into the anterior chamber of adult eyes of the same or different strain (Lewis) survive and differentiate. Light and electron microscopic studies show that the transplants undergo histogenetic differentiation, resulting in the development of neurons and Müller glial cells and formation of nuclear and plexiform layers. Vascular connections develop between the host iris and the retinal transplant. Vessels and nerves, presumably of iridal origin, were seen on the surface of some transplants. Possible manifestations of graft rejection were monitored; signs of tissue rejection in transplants performed in the Long-Evans rats, an outbred strain, were rare and if present they were mild, at least during the survival periods of up to 91 days allowed in these experiments. Transplants into the eyes of Lewis rats were also well tolerated during the survival period. These observations indicate that retinal transplantation to the adult eye of a genetically different host can be successfully achieved and that both embryonic and perinatal retinas are suitable as donor tissue for ocular transplants. The procedure offers ample opportunities for the study of problems related to retinal plasticity.