A randomized, double-blind, placebo-controlled study was performed to assess the analgesic efficacy of intramuscular nefopam hydrochloride after upper abdominal surgery. Patients received either 20 mg nefopam (n = 23) or matching placebo (n = 26), 90 min before surgery, immediately after surgery, and 6, 12 and 18 h after the end of surgery. The 24-h morphine requirements were measured using a patient-controlled analgesia system delivering on-demand intravenous bolus doses of morphine. Pain was assessed using visual analogue scales. Patients receiving nefopam had a mean (± s.e.m.) cumulative morphine consumption of 4.1 ± 0.8 mg in the first hour, compared with 8.5 ± 0.8 mg in the control group (P < 0.01). After 24 h the consumptions were 44.1 ± 7.2 mg and 62.5 ± 6.9 mg respectively (P < 0.05). The pain scores in both groups were similar. This study confirms that nefopam hydrochloride has significant analgesic effects and would be a useful supplement to morphine in the management of postoperative pain.