Glial cell line-derived neurotrophic factor (GDNF) exhibits neurotrophic properties on different types of neurones, including fetal motoneurones and embryonic neurones of sensory ganglia. We demonstrate that chronic injury to the adult rat sciatic nerve induces a rapid up-regulation of GDNF mRNA expression in Schwann cells proximal as well as distal to the injury site, and that expression of this mRNA remains at high levels for at least 5 months after injury. In addition, GDNF mRNA increases and remains high in satellite cells and Schwann cells of the affected L4/L5 DRGs. These findings suggest that GDNF is an important factor in the events that follow upon adult chronic primary sensory neurone injury, and possibly also after adult motoneurone axotomy.