Bath-applied N-methyl-D,L-aspartate (NMA) was found to elicit locomotor electromyogram (EMG) activity in ankle flexor and extensor muscles in an in vitro lumbar cord-hindlimb preparation of the newborn rat. The frequency and burst duration of the NMA-induced rhythmic EMG activity varied in a dose-dependent manner. The locomotor activity was also observed in a mid sagittally split lumbar spinal preparation, in which the frequency was much lower. It is concluded that spinal neurones with N-methyl-D-aspartate (NMDA) receptors are involved in producing locomotor activity in the rat and that each spinal half can generate hindlimb locomotion on the ipsilateral side.