To study the functional role of endogenous basic fibroblast growth factor-2 (FGF-2) during degeneration and regeneration of the sensory system, we have determined the expression and regulation of FGF-2 and FGF receptor (FGFR)-1 mRNAs in spinal ganglia and sciatic nerve during experimental transection and crush injury of the sciatic nerve. In contrast to levels of the FGFR-1 transcript, which is not altered, the level of FGF-2 mRNA is dramatically up-regulated in spinal ganglia after injury. In the proximal and distal nerve stumps both transcript levels are significantly elevated, albeit at different time points. The FGF-2 isoforms are differently up-regulated in spinal ganglia and sciatic nerve following peripheral nerve lesion. The differential response of FGF-2 mRNA and protein and of FGFR-1 mRNA in spinal ganglia and sciatic nerve after lesion is suggestive of different physiological functions: a local reaction at the lesion site where axonal regrowth occurs and a trophic reaction for the degenerating/regenerating sensory neurons.