Clinical feasibility and usefulness of various intraoperative electrophysiological monitoring methods that are widely utilized during neurosurgical operations were critically evaluated. We divided these intraoperative monitoring methods (IOM) into two types; the monitoring methods that enable the surgeons to obtain topographical orientation during operative procedures ('topographical IOM') and those that give them knowledge of the functional state of the nervous system that is involved in the operative procedures ('functional IOM'). It was shown why 'topographical IOM' is reliable and useful, based on our experiences of cortical SEP recordings to localize the central sulcus, and why the present 'functional IOM' is less reliable to guide the surgeons precisely during the operations. We presented some technical methods to cope with these problems in 'functional IOM'. It is necessary to establish a good correlation between the intraoperative changes of the evoked potentials and the pathological changes responsible for these electrical changes as established in clinical electrocardiography.