Immunohistochemical studies with the use of an antiserum against the cocaine- and amphetamine-regulated transcript (CART) peptide-(55-102) showed an abundance of CART-immunoreactive fibers in the mouse dorsal horn laminae I and II. A few CART-positive somata were scattered in the dorsal horn and around the central canal. Intrathecal injection of the CART peptide-(55-102) at doses 3, 10 and 100 ng caused a dose-dependent and significant decrease of paw withdrawal latency; whereas, saline injection was without significant effect. Our results provide the first evidence that CART-immunoreactive fibers are present in the dorsal horn and that the peptide administered intrathecally produces hyperalgesia, as assessed by paw withdrawal latency in mice.