ABSTRACT.Intraoperative monitoring differs from determination of SEP in the laboratory in technique, interpretation and expectations of the technician. In this article, the operating room environment, OR monitoring techniques and interpretation of intraoperative SEP changes will be discussed. Representative cases will be presented which emphasize the importance of rapid and accurate diagnosis. These cases will demonstrate examples of injury to peripheral nerve, brachial plexus, spinal cord, brainstem and cerebral hemisphere which were demonstrated by SEP monitoring.