BACKGROUND Midazolam has been reported to have a spinally mediated analgesic effect. Clinically, single-shot epidural or spinal administration of midazolam has been shown to have an analgesic effect on perioperative pain. In this study, we investigated the analgesic effect of continuous epidural administration of midazolam with bupivacaine on postoperative pain. METHODS Four groups of 20 patients who underwent gastrectomy or cholecystectomy were studied. Continuous epidural infusion of bupivacaine 100 mg (Group C), bupivacaine 100 mg + midazolam 10 mg (Group M10), or bupivacaine 100 mg + midazolam 20 mg (Group M20) in 40 ml per 12 h was started after surgery using the balloon infuser. Group I received intermittent epidural bupivacaine (2.5 mg.ml-1) 6 ml every 2 h. When necessary, an indomethacin suppository and then a single epidural shot of bupivacaine (2.5 mg.ml-1) 6 ml was administered. Blood pressure, heart rate, respiratory rate, analgesic area, analgesia score, and sedation score were monitored for 12 h postoperatively. Memory and frequencies of supplemental analgesia (indomethacin suppositories and epidural bupivacaine) were also checked. RESULTS Group M20 showed a significantly wider area of pinprick analgesia and better analgesia scores than other groups. The need for rescue analgesics were significantly less in Group M20. Sedation and amnesia were more pronounced in Group M20 than the other groups. CONCLUSIONS Adding midazolam (10 to 20 mg per 12 h) to continuous epidural infusion of bupivacaine for postoperative pain can provide a better analgesia, amnesia and sedation than bupivacaine alone.