Efficacy and safety of oral nalbuphine in doses of 15 and 45 mg were compared with those of the standard oral analgesic codeine in single doses of 30 and 90 mg in 153 patients with acute postoperative pain; data on 20 more patients were excluded because they received potentially interfering medications. All patients had pain ranging from moderate to severe in intensity and most had severe pain related to orthopedic procedures or trauma. Estimates of relative potency showed that nalbuphine was three times as potent as codeine. The most common side effect was sedation, which was greatest in patients who received the higher doses of codeine and nalbuphine. The effects of oral nalbuphine are much like those of oral codeine in patients with acute postoperative pain.