The pain components of somatosensory evoked potentials (SEPs) of induced bymedian nerve stimulation were studied with the way of blocking bloodstreamof arm in 12 normal adults.The SEPs following the painful stimuli (0.1msec.square wave pulse) of the right wrist were recorded from the left parietal(C3′) and frontal (F3) scalp with earlob reference electrode.The pressure of40 mmHg above the arterial pressure was given to the right upper arm bysphygmomanometer.The resnlt showed that the P200-N300 components (latency234±13 msec.and 308±23 msec.) of the SEPs persisted and the others disapp-eared when tactile sensation disappeared but pain existed.The morphology ofP200-N300 from F3 was same to that from C3′.It suggested the P200-N300were the pain potentials of median nerve SEPs.