ABSTRACT.There are numerous factors in the operating room that can cause changes and/or artifacts while monitoring somatosensory evoked responses (Chiappa 1983, Nuwer 1986, York 1987). Drugs, anesthetic agents, irrigation, manipulation of the spinal column, changes in the patient's blood pressure and numerous other electrical equipment in the area can all cause changes in the evoked potentials. It is the responsibility of the EP technologist to determine the possible cause of changes when present. The technologist must know what factors can cause changes in the EPs and how to determine the source of artifact. The surgeon must be notified of any critical changes. Intraoperative monitoring can be less stressful and easier for the technologists involved if they are familiar with the surgical procedures, equipment, and medications.