The effects of ambulatory training on the extent and time course of recovery of weight-bearing-stepping in cats spinalized (T12-T13) as adults were investigated. One month after spinal cord transection, 14 of 16 cats were capable of bearing the full weight of their hindquarters with their hind limbs during stepping on a motor-driven treadmill if the tail was pinched or crimped. Of those 14 cats 8 were assigned to a trained and 6 to an untrained group. Trained cats were subjected to 30 min/day of treadmill exercise, 5 days/week. Training was initiated 1 month posttransection and continued until 5 to 7 months posttransection. Daily records were kept on the treadmill speeds used, the time at each speed, and the number of steps that were not full weight bearing. The number of full-weight-bearing steps times treadmill speed was used as a measure of performance. The tail was crimped whenever necessary, but was required less and less as training progressed. Performance plateaus were reached between 25 and 85 days after initiating training (mean = 48 +/- 22 days). Maximum treadmill speeds increased in untrained cats from 0.075 +/- 0.042 m/s 1 month posttransection to 0.240 +/- 0.042 m/s 5 to 7 months posttransection and those of trained cats increased from 0.079 +/- 0.045 m/s to 0.619 +/- 0.133 m/s during this same period. We conclude that a much larger proportion of adult spinal cats are capable of full-weight-bearing stepping than reported, and that training which emphasizes early tail crimping and complete weight bearing at all times results in marked improvements in the locomotor capacity of the hind limbs.