The success of peripheral and fetal neural tissue in promoting outgrowth of axons from the adult mammalian central nervous system has tended to focus attention on local interactions between extending axons and their environment. The contribution to axon regeneration of biochemical and morphological changes in injured neurones is more difficult to evaluate. We report here that long spinal axons of primary sensory neurones are 100 times more likely to regenerate into peripheral nerve grafts if their peripheral axons are also cut. Regenerative behaviour at the axon tip seems to be strongly influenced by inducible events in the nerve cell.