Nalbuphine hydrochloride is an opioid agonist-antagonist that has gained acceptance as a pre-hospital analgesic agent. Nalbuphine has equal analgesic properties to morphine, has a low addiction potential, and can be stored and administered without restrictions, unlike morphine. To date no clinical evidence has been published to support the theoretical difficulty that the action of opioids administered after nalbuphine could be altered or negated. The foliowing case reports highlight 10 patients who received nalbuphine pre-hospital and subsequently required higher doses of opioid analgesia than expected. The discussion summarises the properties of nalbuphine and identifies potential reasons why excessive amounts of opioid analgesia were required. (7Accid Emerg Med 1999;16:29-31)