Epidural buprenorphine was investigated as a postoperative analgesic in a randomized double-blind study of 158 patients given epidural analgesia with mepivacaine or bupivacaine for orthopedic surgery of the lower extremity. At the end of surgery, patients were given either 0.15 mg of epidural buprenorphine (n = 38), 0.3 mg (n = 37) in 15-ml saline, or no further epidural injections (n = 47, control group) after 2% mepivacaine for intraoperative anesthesia. A fourth group (n = 36) received 0.3 mg of buprenorphine in 15-ml saline, after the intraoperative use of 0.5% bupivacaine. The patients rated postoperative pain. The need for additional analgesics as well as side effects were recorded. Analgesia after 0.15 mg buprenorphine was superior to that after no reinjection for 6 hr after surgery (P less than 0.05). Buprenorphine (0.3 mg) was superior both to no reinjection and to 0.15 mg of buprenorphine until the twelfth hour (P less than 0.05). Analgesia after bupivacaine followed by 0.3 mg of buprenorphine was not significantly different than analgesia seen after mepivacaine followed by 0.3 mg of buprenorphine. There was an increase of PaCO2 of 2-5 mm Hg between 1.5-3.5 hr after 0.3 mg of buprenorphine without any evidence for late respiratory depression. Other side effects, e.g., disturbances of micturition, pruritus, nausea, vomiting, fatigue, and headache, were comparably common in all groups. The epidural administration of 0.3 mg buprenorphine may be recommended for postoperative analgesia following orthopedic surgery of the lower extremity.