The control of human locomotion uses afferent information from many sources within the visual, vestibular, and proprioceptive systems: central generators and programmes interacting with peripheral reflexes represent only a portion of the mechanisms involved. Spinal-reflex pathways and descending tracts converge on common spinal interneurons and thus play an integrative role in regulating the input from descending tracts and spinal reflexes. The weakness of studies carried out on humans in this field is due to the fact that human motor-control mechanisms can only usually be surmised by indirect methods such as knowledge gained from animal experiments. Although there are common features between the pattern of activity and the underlying neuronal mechanisms during quadripedal locomotion in cats and that seen during bipedal gait of humans, there are also distinct differences.