We use recombinant retrovirus and adenovirus vectors to deliver neurotrophin genes as a strategy of promoting survival of injured neurons and axon regeneration. The recombinant retroviruses and adenoviruses contain a neurotrophin transgene and a reporter gene, which allows their travel to be tracked in tissue. The virus vectors are injected into the spinal cord and migrate both rostrally and caudally from the site of injection. As the virus migrates from the injection site, a gradient of neurotrophin gene expression is produced. Our theory is that this gradient will encourage injured host cells to project axons towards the site of injection and grafted cells to project axons away from the site of injury.