This study examined the distribution of immunoreactive dynorphin neurons in the lumbar dorsal horn of unilaterally deafferented, colchicine-treated rats. Ipsilateral to a multiple dorsal rhizotomy there was a significant increase both in the number and intensity of staining of dynorphin-immunoreactive cells in laminae I, outer II and V. A comparable change was seen in animals that were deafferented by sciatic nerve section. Enkephalin immunoreactivity was not altered under these conditions. These results indicate that many forms of injury, not all of which result in increased nociceptive input, can increase the level of dynorphin in spinal cord neurons.