The pathological lesion in spinal injury is usually more severe in the central gray matter and spreads centrifugally to surrounding white matter. Opiate antagonists, naloxone, by blocking the pathophysiologic effect of endorphins, should increase both mean arterial pressure and spinal cord blood flow and limit neurologic injury. Naloxone produce increase of lateral column blood flow and ameliorate the central gray matter ischemia. We have investigated the effects of naloxone on histopathological change in cats subjected to thoracic cord contusion. The histopathological evaluation of the injured spinal cords in naloxone-treated cats had less tissue damage than would be observed in time-matched standards. The acute histopathology in saline-treated cats had lesions typical of what we would expect in untreated cats, but the chronic histopathology had slightly better than typical that.