BACKGROUND: Epidural coadministration of opioids and local anesthetics has provided excellent analgesia during the postoperative period. The appropriate amount of epidural morphine for pain control with minimum side effects has been studied. Recently, we gave 6 mg of epidural morphine for 2 day pain control and discovered it was a safe and effective dose like the previous study result. This study was performed to compare postoperative analgesia and side effects according to different loading and infusion doses of morphine with the same total dose. METHODS: Forty-three patients having epiduro-general anesthesia for a hysterectomy were randomly divided into 2 groups. The patients received 2 mg (Control group, n = 19) or 3 mg (Experimental group, n = 24) of epidural morphine by bolus and a continuous epidural infusion was started using a two day infusor containing 4 mg (Control group) or 3 mg (Experimental group) of morphine in 100 ml of 0.125% bupivacaine. Visual analog scale (VAS) for pain, severity of nausea, itching and respiratory depression were assessed at 2, 4, 8, 16, 32 and 48 hours postoperatively. All data was evaluated with unpaired t-test for significances between the two groups. RESULTS: Analgesia between the two groups showed good results. The VAS in the experimental group were higher than the control group in the early postoperative period. Nausea scores were no different between the two groups. The itching scores in the experimental group were lower than the control group at postoperative 16 and 32 hours. No respiratory depression was reported in either group. CONCLUSIONS: This study suggests that different loading and infusion doses of the same total epidural morphine between two groups provided good postoperative pain relief without any differences in side effects.