When glutamate was infected intrathecally, the result is similar to those produced by TPA injected. The involvement of protein kinase C (PKC) in the nociceptive responses in rat dorsal horn neurons of lumbar spinal cord was studied. In test with formalin, a PKC inhibitor (chelerythrine) inhibited dose-dependently the formalin-induced behavior response. Neomycin also inhibited it significantly. But, a PKC activator (12-O-tetradecanoylphorbol-13-ester, TPA) showed reverse effect. When gluatamate was injected intrathecally, we observed the result is smilar to those produced by TPA injection. On the other hand, intrathecal injection of glutamate induced thermal and mechanical hyperalgesia. In Tail-flick test, we examined the involvement of PKC on the glutamate-indeced thermal hyperalgesia. Chelerythrine showed an inhibitory effect and TPA enhanced thermal response. Glutamate decreased the mechanical threshold significantly. A pretreatment of chelerythrine and neomycin inhibited glutamate-induced mechanical hyperalgesia, but the effect of neomycin was not significant. TPA had little effect on the mechanical nociceptive response. These results suggest that the PKC activation through metabotropic receptor at postsynaptic region of spinal cord dorsal horn neurons may influence on the persistent nociception produced by chemical stimulation with formalin, thermal and mechanical hyperalgesia induced by glutamate.