['Both intrathecal sufentanil (ITS) and intrathecal morphine (ITM) improve analgesia in obstetrical or cardiac procedures. From a pharmacokinetic standpoint, combining these two opioids may improve perioperative analgesia. We performed a prospective randomized double-blind study to compare the analgesic efficacy of ITM alone vs a mixture of a low dose of ITS plus ITM for perioperative pain relief in colorectal surgery.', 'Eighty adult patients undergoing colorectal surgery were randomly allocated to receive either 0.4 mg ITM alone or 10 microg ITS plus 0.4 mg ITM before general anesthesia. Intraoperative intravenous sufentanil consumption, postoperative morphine consumption delivered with a patient controlled analgesia device, pain scores, patient satisfaction and adverse effects were recorded for the first 48 hr postoperatively.', 'No differences were observed between groups with respect to intraoperative sufentanil consumption (39 +/- 23 microg in group ITM and 40 +/- 25 microg in group ITS plus ITM, P = 0.85) and in postoperative morphine consumption in postanesthesia care unit (6 +/- 5 mg vs 6 +/- 5 mg, P = 0.59), at 24 hr (26 +/- 17 vs 24 +/- 15 mg, P = 0.59) and at 48 hr (47 +/- 31 vs 44 +/- 22 mg, P = 0.58). Similarly, no differences were observed in regards to pain relief, patient satisfaction and incidence of adverse effects.'] Does low-dose sufentanil potentiate intrathecal morphine for perioperative analgesia after major colorectal surgery?