BACKGROUND: Intravenous (IV) morphine is commonly used for postoperative pain management. Ketorolac has been proposed as a potent analgesic for treatment of moderate to severe pain. The purpose of this study was to determine the equianalgesic dose of morphine and ketorolac using intravenous patient-controlled analgesia (IV-PCA) system in human volunteers. METHODS: Fourty-five patients undergoing elective total abdominal hysterectomy were randomly assigned to receive either morphine (n=22) or ketorolac (n=23) when postoperative pain first increased to 40/100 mm (by visual analogue scale; VAS). Until postoperative pain decreased to 40/100 mm, morphine and ketorolac group received repeated IV boluses of 3 mg of morphine and 18 mg of ketorolac respectively and then followed by a IV-PCA with morphine (basal infusion 0 mg/hr, PCA dose 1 mg/1 ml, lock-out interval 5 min) and ketorolac (basal infusion 0 mg/hr, PCA dose 5 mg/1ml, lock-out interval 5 min). Analgesic efficacy with VAS (0~100 mm), PCA demand ratio and rate, analgesics consumptions, patient satisfaction and side effects were compared. RESULTS: There were no significant differences in VAS, PCA demand ratio and patient satisfaction. Mean 48-hour morphine and ketorolac consumptions were 35 (SEM=2.9) mg and 224 (SEM=16.5) mg, respectively (ratio=1:6.4). Morphine group experienced side effects such as pruritus (45%), nausea and vomiting (41%) and respiratory depression (5%). However, ketorolac group only showed side effects such as nausea and vomiting (26%). CONCLUSION: We concluded the ratio of equianalgesic dose of morphine versus ketorolac using intravenous patient-controlled analgesia (IV-PCA) after total abdominal hysterectomy was 1 versus 6.4.