Using EMG equipment with time locked recording and standard averaging facilities we were able to record a previously poorly defined skin potential. The potential, termed by us the peripheral autonomic surface potential (PASP), was recorded from the palmar surface of the hand and the plantar surface of the foot in 30 normal subjects. The PASP usually consisted of a biphasic potential with an initial negative and a later positive peak. It was elicited by randomly timed electrical stimuli over the median nerve at the wrist. The mean palmar PASP latency was 1.52 +/- 0.13 s and the mean plantar PASP latency was 2.07 +/- 0.16 s. The mean palmar and plantar PASP amplitudes were 479 +/- 105 microV and 101 +/- 40 microV, respectively. A mean sympathetic conduction velocity was calculated to be 1.28 +/- 0.18 m/s. In 5 normal subjects a similar technique was used to record a PASP from the volar surface of the left middle finger. Iontophoresis of atropine into the skin under the recording site abolished the PASP in all subjects. Palmar and plantar PASPs were recorded in 10 diabetic patients. The amplitudes (palmar 179 +/- 158 microV, plantar 17 +/- 16 microV) were significantly reduced compared to normals (P less than 0.001). Five patients with unilateral lumbar or cervical sympathectomy were studied. The PASP was absent or markedly reduced on the side of the sympathectomy in all patients.