Motor evoked potentials(MEP) have been recently introduced as intraoperative monitoring of descending motor pathways. Transcranial electrical or magnetic MEP have been using clinically, but there are still some limitations of using in operating room. Furthermore, according to anesthetic regimens, MEP responses vary significantly. The authors observed the effects of the various anesthetics (thiopental, fentanyl, ketamine, nitrous oxide and isoflurane) on electocortical MEP in a patient who had been previously undertaken electrocortico-graphic grid insertion operation for seizure monitoring. Electromyographic responses were recorded from contralateral arm flexor and extensor using needle type electrode. Most anesthetics except ketamine decreased the amplitude of MEPs reversibly and there were differences in electromyographic responses according to measuring compound muscles.