Nalbuphine is a new partly agonistic antagonistic opioid, that may offer some advantages especially in postoperative pain relief. We compared meperidine (1 mg kg-1) in 100 patients and nalbuphine (0.3 mg kg-1) in 70 patients, administering both agents intravenously after gynaecological operations. Standardised halothane anaesthesia without any opioid was used. After arrival in the recovery room, vigilance (sedation), quality and duration of pain relief were measured by different methods at four different times (0, 15, 30, and 60 minutes). Sedation was significantly more pronounced in the nalbuphine group, but no difference could be found in pain relief and duration between both groups. 6 patients of the n-group showed a short lasting wake-up reaction due to receptor antagonism. 36 patients had to be reinjected at the end of the first hour. We consider nalbuphine to be a safe opioid, however, the marked sedation should be taken into account.