Electromyographic investigation was carried out on the cats in order to analyse the neuronal mechanisms of locomotive movements. 1. When normal unrestrained cats walked gastrocnemius muscle, an extensor, began the activities 77.4 +/- 12.1 msec prior the stance phase. This evidence shows that locomotive movement is preprogrammed in the central nervous system. 2. When hemisection was applied to the spinal cord, reciprocal activities in the antagonistic muscles disappeared for several days. However, the reciprocity resumed again eventually. 3. When two hemisections on both sides were applied at different levels of the spinal cord at intervals of more than 30 days, the cat could not stand for 20-30 days after the second hemisection, but eventually could stand. The reciprocity between the antagonistic muscles were greatly disturbed in many cases. 4. In several cases placing reaction could not be elicited in the two hemisected cats. The possible roles of descending tracts in locomotion were discussed.