Using in situ hybridization histochemistry, we examined the expression of prepro-vasoactive intestinal polypeptide (VIP) mRNAs and preprotachykinin (PPT) mRNAs which coded for substance P (SP) in the rat dorsal root ganglion (DRG) following spinal nerve transection. VIP mRNAs increased dramatically in the DRG neurons after transection of the peripheral branch of the spinal nerve (sciatic nerve), whereas PPT mRNAs showed a gradual decrease for a few weeks. Dorsal rhizotomy or axotomy of the central branch of DRG cells had little influence on VIP-mRNAs and no effect on PPT mRNA expression. These results demonstrated an activation of VIP biosynthesis in the DRG neurons due to axotomy of the peripheral branch, which was opposite to the reaction of PPT mRNA to the same treatment.