The aim of this study was to assess the changes which occurred in the spinal motoneurone pool and in the target muscle after the repair of a specific peripheral nerve, using several clinically appropriate surgical techniques. The motoneurone pool relating to a single muscle was assessed at 50, 100, 200 and 300 days after repair, by means of retrograde axonal transport of the neural tracer horseradish peroxidase. The results indicate that whilst a small portion of the motoneurone population dies after peripheral nerve surgery, the majority of the anterior horn cells appear to have the ability both to survive nerve transection and to form new functional connections after repair. The number of motoneurones associated with the extensor digitorum longus (EDL) after the transection of the sciatic nerve was significantly less than normal, however there was no significant difference in the number of motoneurones labelled after each of the methods of repair. After axonotmesis there was no significant difference in the number of labelled motoneurones compared to normal. There was no significant difference between the mean minimum cell diameters of labelled motoneurones in the ventral horn of the spinal cord after each of the methods of repair. There were alterations in the size, shape, morphology and cytochemical architecture of the fibres of the target muscles after the injury and repair of the sciatic nerve. Although these changes were more marked after the transection of the nerve compared to the less severe crush injury, there was little or no difference in the architecture between the groups which had been repaired by the different methods.