It has been previously demonstrated that members of the neurotrophin family may prevent death of motoneurones following axotomy. Here we report that the expression of mRNA for full-length trkB, which is a signal transducing receptor for BDNF and NT-4, increases transiently in spinal motoneurones after axotomy in adult rats. Thus, transection of the sciatic nerve resulted in markedly increased levels of trkB mRNA in axotomized motoneurones three days postinjury, while the levels had returned to normal within three weeks. The data support that neurotrophins may be important for survival and/or regeneration of motoneurones after axon lesion.