The present study examines the distribution of several neuropeptides, as revealed by immunohistochemistry in the isolated cord. Fetal rat spinal cord was grafted to the anterior chamber of the adult Sprague-Dawley albino rats. After intraocular maturation for 2-3 months, the amount and distribution of somatostatin, neuropeptide Y, substance P, enkephalin, vasoactive intestinal peptide, peptide histidine-isoleucine, calcitonin gene-related peptide and cholecystokinin immunoreactive terminals and cell bodies were analysed using indirect fluorescence immunohistochemistry. The visualization of immunoreactive cell bodies in the grafts was enhanced using a novel intraocular colchicine treatment. In the graft a rich network of somatostatin-positive terminals was found with a high density in well-demarcated areas reminiscent of substantia gelatinosa of the dorsal horn of normal spinal cord. A large number of small- to medium-sized somatostatin neurons was found throughout the grafts without colchicine treatment. This is in contrast to normal spinal cord, where positive neurons were difficult to visualize without colchicine and were mainly confined to the dorsal horn. Neuropeptide Y had a distribution in the grafts similar to that of somatostatin and neuropeptide Y cells were found throughout the grafts without colchicine treatment. In normal spinal cord, neuropeptide Y-positive fibers were found mainly in substantia gelatinosa with a sparse network in the ventral horn. Enkephalin-positive fibers were found throughout the grafts. The distribution of fibers resembled that of somatostatin and neuropeptide Y with distinct zones of high fiber density in well-demarcated areas, whereas the density of nerve fibers in the rest of the graft neuropil was moderate to low. The distribution of substance P was similar to that of enkephalin. After colchicine treatment, both enkephalin- and substance P-positive cell bodies were visualized. In the intact spinal cord both peptides were seen in the entire gray matter with the highest concentrations in the superficial laminae of the dorsal horn. Antisera against calcitonin gene related-peptide, revealed a sparse terminal network and many large cells, which might represent motoneurons. A sparse network of varicose cholecystokinin-immunoreactive fibers was found evenly distributed in the grafts. In normal spinal cord a dense cholecystokinin-positive network of primary sensory afferent origin was found in the dorsal horn. In the grafts cholecystokinin cell bodies were seen after colchicine treatment.(ABSTRACT TRUNCATED AT 400 WORDS)