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Treadmill training with partial body weight support (BWS) is being advocated as a strategy to enhance walking in patients with spinal cord injury (SCI). Clinical reports have not examined the range of sensory inputs that might modulate electromyographic (EMG) output in the legs during training. During passive, manually assisted stepping on a treadmill with partial BWS, we found similar rhythmical EMG activity in the flexor and extensor muscles of the lower extremities in subjects who had chronic, complete thoracic spinal cord injuries and in subject who had incomplete lesions that resulted in minimal motor control and an inability to ambulate. The EMG bursts were temporally synchronized to specific phases of the step cycle, and their amplitudes and durations were modulated by varying the treadmill speed and the level of limb loading. Hip extension at the end of stance often induced involuntary hip flexion that initiated the swing phase. When the incomplete SCI subjects attempted volitional stepping, the EMG bursts in some muscles had a similar waveform but greater amplitude and duration compared to that observed during passive, assisted stepping. This suggests that, as in the model of the cat after a thoracic spinal transection, peripheral sensory inputs that are associated with rhythmical locomotion can enhance the output of lumbosacral neural circuits that contribute to step-like EMG activity, even in the absence of supraspinal descending influences. Attention should be given to optimizing the manipulation of sensory inputs during rehabilitation efforts with body weight supported treadmill training.