['Activation of N-methyl-d-aspartate (NMDA) receptor by reactive oxygen species (ROS) in the spinal cord plays an important role in the development of hyperalgesia in several neuropathic pain models. The study examined the involvement of ROS-NMDA signaling pathway in remifentanil-induced postoperative hyperalgesia.', 'Nociceptive responses were measured by paw withdrawal mechanical threshold (PWT) and paw withdrawal thermal latency (PWL) before and up to day 5 after remifentanil infusion. Spinal delivery of MitoSOX red was performed to detect mitochondrial ROS. Changes in expression of NMDA receptor subunits (NR1 and NR2B) in the spinal cord were analyzed by immunofluorescence and Western blotting. Intraperitoneal injection of phenyl-N-tert-butylnitrone (PBN), a non-selective ROS scavenger, was administrated to investigate the role of ROS in remifentanil-induced postoperative hyperalgesia.', 'Intraoperative infusion of remifentanil induced postoperative mechanical allodynia and thermal hyperalgesia. ROS production, phosphorylated NR1 and NR2B subunits of NMDA receptor were found to be significantly increased in the spinal dorsal horn after intraoperative remifentanil infusion. However, remifentanil-induced postoperative hyperalgesia was suppressed by pretreatment of PBN. In addition, reduction of ROS by PBN prevented enhanced phosphorylation of NR1 and NR2B subunits.'] Does spinal mitochondrial-derived ROS contribute to remifentanil-induced postoperative hyperalgesia via modulating NMDA receptor in rats?