Sympathectomy in animals (monkeys and cats) was found to produce a great and consistent increase in the electrical resistance of the skin, particularly on the foot pad. As the measurements of resistance were found to be useful in the animals for determination of the completeness of sympathectomy, the time required for regeneration after sympathectomy, etc. (Tower and Richter1and Richter2), further observations were made to determine whether sympathectomy has the same effect in man. These observations were made on fourteen patients with surgical sympathectomy performed for therapeutic purposes (migraine, neuralgia, Hirschsprung's disease and Raynaud's disease). METHODS Knowledge of the electrophysiologic behavior of the skin has been obtained almost exclusively from observations made on the palmar and dorsal surfaces of the hands. Accordingly, the present studies were confined to these areas. Electrodes (pure zinc disks and a saturated paste of zinc sulfate and kaolin) applied to the palms and