In addition to alleviate pain there is growing evidence that µ-opioids enhance pain. This problem is known as opioid induced hyperalgesia(OIH).The NMDA receptor is involved in opioid induced hyperalgesia it may be possible to block OIH by cyclooxygenase inhibitors. This has been demonstrated with parecoxib, a COX-II inhibitor, in a experimental pain model.Both COX-1 and COX-2 are expressed in the spinal cord. It would be of interest to investigate whether a COX-1 preferring inhibitor like ketorolac also can reduce opioid induced hyperalgesic in this experimental pain model.