In 18 neurologically normal subjects the corticofugal volleys evoked by anodal and cathodal electrical stimulation of the motor cortex were recorded using epidural electrodes at the high-thoracic and low-thoracic regions of the spinal cord during surgery for scoliosis. At and just above threshold, anodal and cathodal stimulation of the upper-limb area and motor cortex produced a D wave that propagated to the low-thoracic region. The stimulus intensity required to produce D waves was significantly lower with anodal stimulation. I waves were recorded at higher stimulus intensities than the D wave but not more readily with cathodal stimulation. There was no significant difference in the extent to which stimulus intensity had to be increased above D-wave threshold to produce I waves with the two stimulus polarities, and the number of I waves was the same when the stimulus was increased by the same amount above D-wave threshold. After withdrawal of isoflurane, I waves could not be recorded when the stimulus intensity was below D-wave threshold with either stimulus polarity. Anodal stimulation over the upper-limb area remained more effective than cathodal stimulation in producing both D and I waves. These results indicate that, at threshold, regardless of anaesthesia, anodal and cathodal stimuli access upper-limb corticospinal neurons directly at a similar site, the anodal stimuli being more effective. In addition, the results suggest that some corticospinal neurons in the upper-limb area of motor cortex have projections to lumbar segments.