The NMDA receptor has been reported to be involved in opioid tolerance. Adj
uvant subcutaneous infusion treatment with (very) low-dose ketamine, a NMDA
receptor antagonist, improves analgesia and at the same time appears to re
duce morphine tolerance. Three cases are presented. (C) 1999 International
Association for the Study of Pain. Published by Elsevier Science B.V.