Under normal circumstances peripheral nerves maintain stable con nections with their targets throughout the life of an animal. Despite this appearance of stability, many of the cellular behaviors associated with growth persist in mature neurons: They may continuously remodel their connections (Purves & Voyvodic 1987), produce and transport to the nerve terminal many of the molecules needed for nerve growth (Lasek et aI1984); and they elongate considerably during body growth. On injury, nerve fibers distal to the lesion degenerate by the process known as Wallerian degeneration, and the neurons reinitiate axonal growth with its attendant metabolic changes. The cellular processes underlying degeneration and regeneration are the subject of this review.