BACKGROUND: Postoperative pain is a major contributing factor to immune dysfunction related to changes of peripheral neutrophils, lymphocytes and monocytes. The aim of this study is to compare alterations in peripheral white blood cells perioperatively in patients under intravenous patient controlled analgesia (IVPCA) with intra-articular patient controlled analgesia (IAPCA) after general or spinal anesthesia, or epidural patient controlled analgesia (EPCA) after combined spinal epidural anesthesia for knee replacement surgery. METHODS: Thirty-three patients with IVPCA and IAPCA after general anesthesia (group 1), 33 patients with IVPCA and IAPCA after spinal anesthesia (group 2), and 34 patients with EPCA after combined spinal epidural anesthesia (group 3) were reviewed. The number of peripheral neutrophils, lymphocytes and monocytes were counted preoperatively, immediate postoperatively, on the first, third and fifth postoperative day. RESULTS: There were significant increases in neutrophils, decreases in lymphocytes, and increases in monocytes postoperatively in all the groups. However, there were no differences among the groups in three subtypes of white blood cells, except significantly low value of monocytes in the group 1 compared to that of group 2 immediate postoperatively. CONCLUSIONS: The technique of anesthesia and postoperative pain control did not influence to the changes of subtypes of circulating white blood cells in patients underwent knee replacement surgery.