BACKGROUND: Recent advances in the understanding of acute pain mechanisms show that inflammatory pain is the result of changes in the nervous system. Preemptive analgesia may prevent nociceptive inputs generated during surgery from sensitizing central neurons and, therefore, may reduce postoperative pain. In previous studies, we demonstrated that modest dose of i.v. morphine infusion before surgical incision significantly decreased postoperative pain. We studied whether or not intravenous fentanyl infusion before induction could affect postoperative pain and analgesic demands, when compared with intravenous fentanyl infusion at 30min after skin incision. METHODS: Female patients scheduled for total abdominal hysterectomy were randomly assigned to one of two groups of prospectively studied in a double-blind manner. Group I (n=14) and II (n=15) received intravenous fentanyl (4 g/kg) before induction of anesthesia and at 30min after skin incision, respectively. Postoperative pain relief was provided with epidural fentanyl and local anesthetics from a PCA system (Medex Walkmed). Postoperative visual analogue pain scores, analgesics requirements and side effects were examined and compared between groups for postoperative 2 days. RESULTS: VAS at rest were significantly less in group I than in group II 1hrs after surgery (p<0.05). VAS on movement were significantly less in group I than in group II 1hr (p<0.01) and 6hrs after surgery (p<0.05). Patient-controlled analgesics consumption in group I was not significantly less than in group II for postoperative 2 days. CONCLUSIONS: Administration of intravenous fentanyl before skin incision has better outcome in preemptive analgesia than that of 30 min after skin incision. But, further studies would be needed to evaluate preemptive effect of i.v. fentanyl.