The development of quadrupedal walking in infant Japanese macaques (Macaca fuscata) was studied on the basis of their footfall patterns. Lateral views of the walking of 5 monkeys were taken by a video-camera and the timing of touchdown and liftoff was recorded. The total number of trials was 435. The change of footfall patterns during development was complicated. Four stages could be discerned, as in behavioural studies. In the first stage, there was a wide variation. The dominant patterns were the diagonal sequence which included any type of couplet in the second stage and trot in the third stage. There were two groups of footfall patterns in the fourth stage which were the diagonal sequence – diagonal couplet and the lateral sequence – lateral couplet. It seems that the stages reflect aspects of the development of both the neural system and the musculoskeletal sys