Single shock excitation of the cat''s lumbar sympathetic chain evokes brief negativity of the ipsi-lateral hind footpad relative to skin of back, ear or leg. The potential appears related to sweat gland activation because it occurs only where sweat glands are concentrated, i.e., the footpad; it is abolished by sudorific blocking agents (atropine); and outflow from cord and chain is the same for electrical response and occult sweating. The magnitude of the potential is quantitatively related to numbers of postganglionic fibers activated; preganglionic stimulation reveals fractionation (Sherrington) of ganglion cells. The sudomotor effector response is compared with mechanical responses of muscle. Sudomotor potentials differ from action potentials because they fuse and summate on repetitive stimulation. They are not to be construed as a response of a glandular membrane comparable to the membrane of muscle, but there is a close parallel between the electrical response of sweat glands and the mechanical response of muscle. Postganglionic neurons were found in ganglia L6, L7 and S1, also S2 in a fixed lumbosacral plexus. Their axons reached the footpad through sciatic and plantar nerves. Preganglionic outflow was found in the white rami T12-L4, and appeared independent of plexus constitution. Some preganglionic fibers make sudomotor connections in only 2 ganglia and thus evoke topographically restricted sweating. Some preganglionic fibers activating sweat glands also activate other sympathetic effectors. Such fibers evoke functionally diffuse discharge.