The effects of sevoflurane (S) (0.5%, 1.5%, and 2.5%) on the spinal dorsal horn wide dynamic range (WDR) neuronal activity were studied in either spinal cord intact or spinal cord transected cats. Extracellular activity was recorded in the dorsal horn from single WDR neurons responding to noxious and non-noxious stimuli applied to the cutaneous receptive fields on the left hind paw foot pads of intact or decerebrate and spinal cord transsected (L1-2) cats. When BK 10 micrograms was injected into the femoral artery ipsilateral to the recording site as the noxious test stimulus in the spinal cat, 7 of 8 WDR neurons gave excitatory responses which were not depressed by sevoflurane 0.5% and 1.5% but were depressed significantly by 2.5%. On the other hand, when BK 10 micrograms was injected into the femoral artery ipsilateral to the recording site in the intact cat, 6 of 13 WDR neurons (46%) gave excitatory responses, which were significantly depressed by sevoflurane 0.5%, 1.5% and 2.5%, and 7 of 13 WDR neurons (54%) gave inhibitory responses, which were significantly depressed sevoflurane at 0.5%, 1.5%, and 2.5%. In conclusion, we have found that sevoflurane reduces the excitation as well as the inhibition of dorsal horn WDR neuronal activity induced by BK injection.