The effects of isoflurane (0.5% and 1.5%) 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 foot pads of intact or decerebrate, spinal cord transected (L1-2) cats. When bradykinin (BK) 10 micrograms was injected into the femoral artery ipsilateral to the recording site as the noxious test stimulus in the spinal cat, all of 17 WDR neurons gave excitatory responses which were not depressed by 0.5% isoflurane but were depressed significantly by 1.5%. On the other hand, when the injection of BK 10 micrograms into the femoral artery ipsilateral to the recording site was used in the intact cat, 13 of 24 WDR neurons (54%) gave excitatory responses, which were significantly depressed by 0.5% and 1.5% isoflurane, and 11 of 24 WDR neurons (46%) gave inhibitory responses, which were significantly depressed by 0.5% and 1.5% isoflurane. We have found that isoflurane reduces the excitation as well as the inhibition of dorsal horn WDR neuronal activity induced by BK injection.