BACKGROUND: Morphine for the intravenous patient controlled analgesia (IV-PCA) provides effective postoperative pain control, but it has side effects such as itching, nausea and vomiting. Meanwhile, butorphanol, a synthetic potent agonist-antagonist narcotic with low incidence of adverse side effects and minimal addiction, produce adequate analgesia for postoperative pain. The purpose of this study was to compare the suitability of butorphanol combining with or without morphine with that of morphine in terms of relieving postoperative pain and incidence of side effects. METHODS: Sixty ASA physical status I or II female patients undergoing total abdominal hysterectomy were randomly allocated into one of three groups according to type of drug used (n=20 for each group). The groups were divided to group M (morphine 100 mg), group M B (morphine 50 mg+butorphanol 10 mg) and group B (butorphanol 20 mg). Drugs for each group mixed with 90 ml of normal saline (total amount: 100 ml) for infusion. Loading dose, PCA dose, lockout interval, mode of infusion was 0.05 ml/kg, 0.02 ml/kg, 8 minute, and PCA only, respectively. In each group, visual analog scale (VAS), pain score, sedation score, degree of satisfaction, total amount of drug used, history of attempt/injetion and incidence of side effects were checked. RESULTS: There were no significant differences in analgesic effects and degree of satisfaction among three groups, but incidence of side effects (especially pruritis) were less in group M+B and B compared with group M (p<0.05). CONCLUSIONS: Butorphanol showed comparable postoperative pain relief and marked less side effects compared with morphine. Butorphanol was considered as a useful drug for postoperative pain relief using IV-PCA.