Glycine, GABA, aspartate and glutamate are putative neurotransmitters in the mammalian spinal cord. The distribution of these amino acids was determined in the rat spinal cord. Transversely, the highest levels of glycine, aspartate and glutamate were in the intermediate and ventral gray; whereas, the highest levels of GABA were in the dorsal gray. Longitudinally, the highest levels of GABA and aspartate were in the thoracic and lumbar segments; whereas, the highest levels of glycine and glutamate were in the cervical and thoracic segments, respectively. In general, the distribution of these amino acids is similar to that reported for the cat, dog and human.