The injury was performed with 600 g-cm/weight on the spinal cord of 40 cats with T8-9 laminectomy in this study. Ten cats were given 10 mg/kg naloxone i.v. 1 h after injury. Ten cats were given 2 mg/kg thyrotropin-releasing hormone (TRH) i.v. 1 h after injury followed by 1 mg/kg per hour for 4 h. Intravenous lidocaine was begun 30 min after injury in ten cats, administered as 1.5 mg/kg over the initial 5 min, 3 mg/kg over the next 30 min and 1 mg/kg every 30 min for 4 h. The remaining ten cats were given only saline (control group). TRH-treated cats showed significantly better histopathological scores than either naloxone- or lidocaine-treated animals (KW:13.65, P less than 0.50).