Twenty patients scheduled for elective major abdominal surgery were matched into two groups with regard to age, sex, height, body weight, and surgical procedure. Both groups received general anesthesia plus lumbar epidural analgesia with similar loading doses of bupivacaine 0.5% (23.1 +/- 1.0 and 23.3 +/- 0.8 ml) (mean +/- SEM) followed by continuous infusion of plain bupivacaine 0.5% (8 ml/hr) plus, in one group, epidural morphine (0.5 mg/hr). Pain score on a 5-point scale and sensory analgesia (pin prick) were assessed hourly for 16 hours after skin incision. If sensory analgesia decreased more than 5 segments from preoperative levels or if pain scores reached 2 (moderate pain), the patients were removed from the study, and pain was treated with other methods. Preoperative mean (+/- SEM) sensory levels of analgesia were similar in the bupivacaine and the bupivacaine-morphine groups (T3.4 +/- 0.5 and T3.3 +/- 0.4, respectively). In the group receiving only bupivacaine, sensory analgesia regressed over time with a simultaneous increase in pain score. Thus, within 10 hr after skin incision, seven patients in this group were discharged from the study, and 16 hr after incision only one patient maintained initial level of sensory analgesia. In contrast, each patient receiving bupivacaine plus morphine had stable sensory analgesia and was completely free of pain as indicated by a mean pain score of zero during the 16-hr observation period. Thus epidural morphine may improve pain relief and maintain analgesia during continuous epidural bupivacaine administration after abdominal surgery.