The spinal cord of the eel, Anguilla, recovers function rapidly after it has been completely transected. At transection, the excitability of central pattern generating circuits in the distal denervated segments increases to such a level that undulatory movements can occur spontaneously. When this elevated neuronal activity was reduced locally, just caudal to the transection, by chronic blockade of the NMDA receptor, the normally rapid behavioural recovery was retarded. The NMDA-treated fish overcame cordotomy more slowly than untreated animals, and axons did not extend as far into the denervated cord as in untreated counterparts, until later stages of recovery. These results suggest that central pattern generating activity may facilitate axonal growth in spinal cord regeneration.