The effect of the opiate antagonist naloxone on the functional recovery of rats injured with a 10 g-cm impact to the spinal cord at the T-3 level is studied. Sixteen rats were treated with 0.8 mg of naloxone in an intraperitoneal bolus 45 and 120 minutes after injury, 16 rats were given 4 mL of saline instead of naloxone, and 16 rats were neither injured nor treated. To asses weekly the motor recovery of the injured animals, the inclined plane method was employed. After the 10-week assessment period, naloxone-treated animals showed a significantly better performance on the inclined plane than saline-treated animals. Naloxone may be useful for the treatment of spinal cord injury although its mechanism of action remains unknown.