Injury to peripheral nerves causes a neuropathic pain which is difficult to relieve, but the underlying mechanism remains largely unknown. In previous studies we reported that voltage-gated potassium (Kv) channel alpha genes are downregulated in the dorsal root ganglia (DRG) following chronic constriction of the sciatic nerve [Kim et al. (2002)], suggesting a relationship between electrical abnormalities of the injured neurons and Kv gene expression. Here, we examined expression of the Kv 1.2, 1.4, and 4.2 genes in the DRG following transection of the sciatic nerve, and investigated the effect of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) on expression of those mRNAs, using the reverse transcription-polymerase chain reaction. Expression of these mRNAs was reduced by axotomy and by exposure to BDNF, and NT-3 treatment. However no significant change was detected following NGF treatment. Our findings suggest that downregulation of Kv channel gene expression in DRG neurons by neurotrophins may play an important role in long-term changes of neuronal excitability following nerve injury.