Two weeks following chronic partial constriction of rat sciatic nerve, the perineurium was disrupted and a neuroma had formed at the constriction site in all nerves (n = 5). Axon counts demonstrated an 84-99% and a 62-84% decrease in myelinated and unmyelinated axons respectively, distal to the lesion. Distally, the majority of surviving myelinated axons had diameters of less than 5.0 microns. There was considerable disparity in fiber loss from animal to animal, but similar behavioral changes were demonstrated by all animals. These results are discussed with reference to previously published data and possible mechanisms underlying the behavioral manifestations of this neuropathy model.