This study evaluates the efficacy and side effects of a low dose of epidural morphine combined with clonidine for postoperative pain relief after lumbar disc surgery. In 36 of 51 patients who accepted the procedure, an epidural catheter was inserted (L1-L2 level). General anesthesia was induced with propofol and sufentanil, and maintained with sevoflurane in O2/N2O. After emergence from anesthesia, epidural analgesia was initiated according to two randomly assigned protocols: 1 mg of morphine with 75 microg of clonidine (Group M) or 12.5 mg of bupivacaine with 75 microg of clonidine (Group B), in 10 mL saline. Piritramide was administered during the first postoperative 24 hours using a patient-controlled analgesia device (PCA). The following parameters were recorded: piritramide consumption during the first 24 hours; pain at rest during the first postoperative hours (D0), during the first night (D1), and during the first mobilization; [visual analogue scale (VAS)]; and the occurrence of drowsiness, motor blockade, respiratory depression, nausea, vomiting, itching, micturition problems, and bladder catheterization during D0 and D1. Epidural administration of morphine-clonidine significantly improved postoperative pain relief and reduced piritramide consumption as compared to epidural bupivacaine-clonidine. Side effects did not differ between groups except for a higher incidence of micturition problems in Group M during D1. The occurrence of bladder catheterization was not significantly higher in that group. We conclude that a low dose of epidural morphine combined with clonidine offers a better postoperative analgesia than does bupivacaine-clonidine. The excellent analgesic conditions were obtained at the expense of a higher incidence of difficulties in initiating micturition.