Pain is one of the most prevalent conditions limiting productivity and diminishing quality life and therefore is an important medical problem. Reactive oxygen species (ROS) are critically involved in the generation of various painful conditions, including neuropathic and inflammatory pain. Pain induced by capsaicin, a pungent agent found in red chili pepper, has well defined peripheral and central components, making it a good model for studying the role of ROS in different components of pain. Therefore, it is important to understand the mechanisms underlying capsaicin-induced pain, which then can lead to the development of new treatment paradigms. To further explain the underlying mechanisms of oxidative stress in persistent pain, we examined the effects of ROS scavengers, phenyl-N-tert-butylnitrone (PBN) and 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxyl (TEMPOL) after intradermal capsaicin treatment. Capsaicin was injected intradermally (25 ėg in 5 ėl) into the hind paw and mice developed primary and secondary hyperalgesia. Systemic administration of PBN (100 mg/kg i.p.) or TEMPOL (300 mg/kg, i.p) alleviated capsaicin-induced secondary, but not primary hyperalgesia. Intrathecal injection of PBN (200 ėg in 5 ėl saline) or TEMPOL (500 ėg in 5 ėl saline) also significantly alleviated capsaicin-induced secondary hyperalgesia, thus suggesting the antihyperalgesic effect of PBN and TEMPOL is targeted to the spinal cord. Since the capsaicin-induced secondary hyperalgesia is due to central sensitization, the present data suggests that ROS play an important role in central sensitization and thus in secondary hyperalgesia.