Recent evidence suggests that surgical incision and other noxious perioperative events may induce prolonged changes in central neural function that later contribute to postoperative pain, Inhibition of these changes may be of value in the reduction of postoperative pain. Several clinical studies have shown that pretreatment with local anesthetics, opioids, NASAIDs and N-methyl-D-aspartate(NMDA) antagonist are effective in relieving postoperative pain. We compared the efficacy of pre-emptive and post-incisional epidural analgesia with morphine 2 mg in 0.25% bupivacaine(8 ml) on the postoperative pain. Seventy patients (ASA physical status I, 2) scheduled for elective lower abdominal surgery were randomized to one of two groups of equal size and prospectively studied in a double-blind manner. Group I received epidural morphine(2 mg, in 8 ml 0.25% bupivacaine) before surgical incision followed by epidural normal saline(8 ml) just before termination of the surgery. Group 2 received epidural normal saline(8ml) before surgical incision, followed by epidural morphine(2 mg, in 8 ml 0.25% bupivacaine) just before termination of the surgery. Anesthesia was induced with thiopental sodium(4~6 mg/kg) and maintained with N2O/O2 and enflurane. Paralysis was achieved with pancuronium. Percentage of maximal possible effect(MPE) was significantly higher(P<0.05) in group 1 (85.3%) than in group 2 (70.8%). Secondary analgesic requirement was less in group 1(9/35 patients, 25.7%) than in group 2 (15/35 patients, 42.9%). Visual analog scale pain and mood score and Prince-Henry pain score are not significantly different between two groups. We conclude that pre-emptive epidural analgesia with morphine and bupivacaine may be more effective in relieving postoperative pain than post-incisional analgesia in lower abdominal surgery.(Korean J Anesthesiol 1995; 29: 895~902)