Forty-six patients undergoing major abdominal surgery were given postoperative epidural analgesia for four days with bupivacaine-sufentanil or bupivacaine-morphine. Both groups received a bolus of 8 ml bupivacaine 0.5% followed after 30 minutes by an infusion of 20 ml/h bupivacaine 0.1%. The sufentanil group (group A: 21 patients) received a loading dose of 50 micrograms sufentanil and a continuous infusion of 5 micrograms/h sufentanil. The morphine group (group B: 25 patients) received no loading dose of morphine but only a continuous infusion of 0.5 mg/h morphine. Both regimens provided excellent analgesia, but the frequency of respiratory depression was much greater in group A (33% versus 4% in group B). This respiratory depression occurred in the first hours postoperatively, when the patients were still in the post-anesthesia care unit. There was also a high incidence of hypotension after the loading dose of bupivacaine 0.5%. Although we noticed a large incidence of pruritus, no patient needed naloxone reversal. In view of these side effects we recommend a lower loading dose of both bupivacaine and sufentanil.