Abstract Axons were counted in rat dorsal roots three segments cranial and three segments caudal to a spinal hemisection done at birth. The animals were placed in three groups: (1) hemisected (HEMI), (2) hemisected and given nerve growth factor (NGF) daily (HEMI + NGF) and (3) hemisected and given antibodies to NGF daily (HEMI + anti-NGF). They were sacrificed at 1 month. In the HEMI and HEMI + NGF groups, there were 20% and 13% more unmyelinated axons, respectively, in roots of the operated side. We interpret these differences to be the result of sprouting of unmyelinated axons as a result of denervation, and exogenous NGF does not seem to affect the response. By contrast, the unmyelinated axon responses in HEMI + anti-NGF animals are different. These animals have approximately 7% more unmyelinated axons on the denervated side and 50% more axons on the normal side than in the other animals we studied. The results on the anti-NGF animals are interpreted as indicating sprouting in response to a chemical denervation caused by NGF removal and the response is more dramatic on the unoperated side.