The safety and efficacy of single intramuscular doses of dezocine (10 or 15 mg) were compared with butorphanol (2 mg) and placebo in 157 patients with moderate to severe postoperative pain. A verbal pain intensity scale, an analog pain intensity scale, and a verbal pain relief scale were used to record the patients' subjective assessments. The results of this study indicate that a single 10 or 15 mg intramuscular injection of dezocine is safe and more effective than placebo for four to six hours, respectively, in the treatment of moderate to severe postoperative pain (P less than .05). During the first hour of treatment the pain relief afforded by 2 mg of butorphanol was significantly greater than that afforded by 10 mg of dezocine (P less than .05), but both doses of dezocine provided long-lasting relief. The scores on all three efficacy scales were highest with the 15 mg dose of dezocine after the first hour, while the 10 mg dose of dezocine and butorphanol were compared during this period. Nausea and vomiting were the most commonly reported side effects; injection site reactions were reported more frequently in the butorphanol group.