Epidural sufentanil 50 micrograms was compared with intramuscular buprenorphine 0.3 mg for postoperative pain relief. Patients were assigned randomly to one of two treatment groups and received both an intramuscular and epidural injection, one of which was a placebo. Onset of pain relief was faster and quality of analgesia superior during the first 2 hours in the patients who received epidural sufentanil but the duration of analgesia was longer in the buprenorphine group. Cardiovascular variables remained stable in all patients and no respiratory depression was observed. Side effects were more frequent following buprenorphine.