Spinal cord monitoring during operation is of increasing importance in the prevention of injury. However, there is no direct monitor of the motor tracts available. We have reported a system using direct stimulation of the area overlying the motor tract between the intermediolateral sulcus and the dentate ligament in cats. This produces a 100-m/second signal with later components, which is abolished by section of the motor area, but not by section of the dorsal columns or the anterior quadrant of the spinal cord. Such stimulation also produces motor movement when the correct frequency is used. We now report the first application of this technique in humans, in whom we found the same 100-m/second signal, as well as slower components. We were able to elicit distal limb motor movement with stimulation of the motor tract area, but not with stimulation of the dorsal column area. This technique can be used either in open surgical cases or percutaneously and should provide an additional valuable technique for assessing spinal cord function.