Since buprenorphine has been reported to be effectively analgesic yet free of addiction potential, two single-dose, double-blind, parallel studies were conducted to compare its analgesic activity and safety with those of morphine. The patients in each study consisted of patients experiencing moderate to severe postoperative pain. They were treated with an intramuscular injection of either 0.2 or 0.4 milligram of buprenorphine (Study I) or 0.15 or 0.30 milligram of buprenorphine (Study II) compared with 5.0 or 10.0 milligrams of morphine in both instances. Patients were interviewed prior to drug treatment and at 10, 20 and 30 minutes, and one, two, three, four, five and six hours postdose to determine pain intensity and relief. The degree of sedation, vital signs and side effects were evaluated. Buprenorphine generally appeared comparable to morphine in the onset and duration of action and in side effect liability.