Nalbuphine is an agonist/antagonist analgesic. After parenteral administration of 'usual' doses it is approximately equipotent in analgesic activity to morphine on a weight basis. In studies in patients with moderate to severe pain, usually following surgery, the characteristics of analgesia with nalbuphine were comparable to those seen with equianalgesic doses of morphine or pentazocine. It also appears to produce satisfactory anaesthesia when used as a component of a 'balanced' anaesthesia technique, although a relatively low 'ceiling' effect for reduction of anaesthetic requirements with nalbuphine may limit its usefulness in this regard. As with other agonist/antagonist analgesics, a 'ceiling' effect to nalbuphine-induced respiratory depression is also seen, beyond which further depression does not readily occur. However, with usual analgesic doses, respiratory depression seen with nalbuphine is comparable to that with morphine. Important haemodynamic changes have not occurred after usual doses of nalbuphine, even in patients with cardiac disease. Like other agonist/antagonist analgesic drugs, the abuse potential of nalbuphine seems relatively low, but only wider clinical use for longer periods can establish this with certainty. Thus, nalbuphine appears to offer a useful alternative to morphine in patients with moderate to severe pain.