The authors reported the changes of spinal-cord-evoked potential following impact injury by the weight dropping technique (Allen's method). The correlation between the change in amplitude of the spinal-cord-evoked potential after injury, and the prognosis for motor recovery of the legs was discussed. The spinal cord of adult dogs was traumatized by the weight dropping technique (Allen's method) at the level of Th10. The trauma consisted of a 300 gm-cm impact injury, a 400 gm-cm impact injury, and a 500 gm-cm impact injury. The spinal-cord-evoked potential following direct stimulation of the spinal cord was recorded from the epidural space for 5 hours. The recording electrode was located cephalad to the site of the impact injury. The stimulating electrode was located at the caudal site of the injured area. The motor function of the dogs was observed by clinical scale for rating hind limb motor function (modified Tarlov score) for one month after the trauma. The recovery of the spinal cord evoked potential following impact injury by the weight dropping technique could be estimated one hour after trauma in the 300 gm-cm injury, 30 minutes after trauma in the 400 gm-cm injury and immediately only after trauma in the 500 gm-cm injury. A greater reduction of amplitude of I potential was noted with the higher energy injury (p less than 0.05). There was no parallel correlation between the change in amplitude of the spinal cord evoked potential after injury and the prognosis for motor recovery of legs. However, the changes in amplitude corresponded moderately well to the prognosis of motor function.