 Until today, however, there is no standard-monitoring to specifically reflect the analgesic component of general anesthesia. Because over dosage as well as under dosage of opioids e.g. remifentanil may increase postoperative pain, the development of a depth-of-analgesia monitor is not only desirable but necessary. Quality and safety of general anesthesia are of major clinical importance and can be improved by limiting the administration of opioid analgesics to the minimum dose needed. This study therefore examines the quality of the monitoring technique, i.e. the sensitivity and specificity in assessing the level of analgesia during general anesthesia under standardized conditions. 