142 patients scheduled for total hip arthroplasty were randomized to receive treatment with ketamine infusion during anaesthesia, preoperative oral pregabalin, combined ketamine and pregabalin, or placebo of both. The purpose was to determine if the combination of drugs was more efficacious than either alone. All patients received patient-controlled morphine analgesia postoperatively, and were evaluated for cumulative morphine consumption, pain at rest and on movement, side-effects experienced and secondary hyperalgesia for the first 48 postoperative hours. Compared to placebo, all other groups significantly reduced cumulative morphine dose, although there was no significant reduction in pain or opioid-related side-effects in any group.