The safety and efficacy of buprenorphine and morphine as postoperative analgesics for children were compared in 60 boys and girls 4 to 14 years old having elective orthopedic operations on upper or lower extremities. The drugs were given in a double-blind manner initially intravenously and thereafter by sublingual buprenorphine or intramuscular morphine administered as required to relieve pain until the third postoperative morning. The IV dose needed to achieve complete initial analgesia was 5.2 +/- 2.8 micrograms/kg buprenorphine and 166 +/- 100 micrograms/kg morphine. The duration of effect was significantly longer with buprenorphine than with morphine, 248 +/- 314 and 114 +/- 109 minutes, respectively (P = 0.03). The most common side effects were nausea and vomiting (28 and 16%) and urinary retention (21 and 19%) in the buprenorphine and morphine groups, respectively. Analgesia with sublingual buprenorphine was as effective and reliable as with intramuscular morphine but a longer duration of action could not be demonstrated.