Twenty-five patients with moderate to severe pain after major upper abdominal surgery chose to receive nalbuphine on demand from a Cardiff Palliator for pain relief. An initial i.v. injection of nalbuphine 20 mg was followed by 5 mg given over 90s in response to each successful demand. A maximum of 20 doses (100 mg) hr-1 of nalbuphine was available, plus additional bolus doses. Twelve patients obtained good pain relief and completed the 5 hour observation period. 13 patients withdrew from the study, 8 because of inadequate pain relief and 2 because of side-effects. At least half the patients who complained of inadequate pain relief at the time had no subsequent memory of the events. Despite high dosage in some cases (up to 200 mg in an hour) no clinically important cardiovascular or respiratory effects were observed.