Embryonic cortex from 19-day fetuses was transplanted in a medial frontal cortex wound cavity of 105-day-old male rats. Nissl-stained tissue revealed little internal laminar organization. Graft sections impregnated by the Loyez method exhibited bands of myelinated fibers surrounding implants as well as long-interconnecting and swirl-like fiber fascicles within the implant. Tissue processed histochemically for acetylcholinesterase and choline acetyltransferase revealed enzyme-positive fibers and cell bodies within the grafts. Cytochrome oxidase histochemistry revealed regional variations in the metabolic activity of the grafts. In summary, although our frontal cortex grafts exhibit many of the morphological features seen in intact frontal cortex, the organization of these components within the implant is dissimilar to normal cortical tissue.