The present experiment examines astrocytes in fetal cerebral cortical homografts to adult rat spinal cords. The purpose of this study is to determine if astrocytes are structurally organized within the graft. Also, the presence or absence of astrogliosis may be an indicator of the metabolic status of the graft. Embryonic cerebral cortex was taken at 14 days gestational age and transplanted into adult spinal cord at the level of the sixth thoracic vertebra. The homografts were examined at the light and electron microscopic levels from 7 days postimplantation (PI) to 6 months PI with glial fibrillary acidic protein antiserum which is a specific immunohistochemical marker for astrocytes. At 7 days PI, immunoreactive astrocytes were present only at the periphery of the graft and appeared to be associated with blood vessels. By 30 days PI, normal protoplasmic astrocytes were present throughout the graft. No hypertrophied astrocytes are present at 30 days PI, but the numerical density of astrocytes is greater than that of normal cerebral cortical gray matter. Fibrous astrocytes are present in the periphery of the implant and many of these astrocytes extended their processes between the host and the graft. Occasional glial scarring is observed between the gray matter of the host and graft, but generally no glial scar occurred in the interface between the graft and the host gray matter. By 45 days PI, hypertrophied astrocytes can be seen in the graft, but are confined in this age group to perivascular regions.(ABSTRACT TRUNCATED AT 250 WORDS)