Lignocaine has been used successfully to treat burn pain and neuropathic pain. We have conducted a randomized, double-blind trial to assess the morphine-sparing effect of intravenous lignocaine in patients with acute pain. After major abdominal surgery, patients were treated with post-operative patient-controlled intravenous analgesia in two groups: group M (n = 25, morphine 0.2 mg mL−1) and group ML (n = 25, morphine 0.2 mg mL−1 plus lignocaine 3.2 mg mL−1). The patient-controlled analgesia system was programmed to deliver a 5 mL bolus with a 50 mL per 4 h limit; the lockout time was 10 min. Both groups closely resembled each other in terms of demographic data, pain intensity, cumulative morphine dose and the morphine-associated nausea, vomiting and pruritus. However, the sedation scores in group ML patients during the first post-operative day were significantly greater than those in group M. The incidence of lignocaine-related lightheadedness and dry mouth was also significantly greater in group ML than in group M. It was concluded that the addition of lignocaine 3.2 mg mL−1 to morphine 0.2 mg mL−1 given via patient-controlled analgesia system does not provide a post-operative morphine-sparing analgesic effect.