AT PRESENT the electrical resistance of the skin is widely employed in measuring the activity of the sympathetic nervous system.1 Its use is based on the fact that the electrical resistance offered by the body to the passage of a minute imperceptible direct current is a measure of sweat-gland activity, which in turn is controlled by the sympathetic nervous system. In this laboratory and elsewhere, the mapping of bodily areas of relatively high and low skin resistance has been used to diagnose peripheral nerve injuries, to follow the progress of nerve regeneration after nerve suture, to localize the level of lesions of the spinal cord or roots, to determine the effectiveness of sympathectomy or procaine paravertebral blocks, and to aid in determining preoperatively the desirability of sympathectomy in various peripheral vascular diseases. In addition, it has been widely used in less clinically applicable experimental work. The present