SUMMARY The upper limbs of 10 healthy subjects were cooled and then warmed over physiological temperature ranges. The compound action potentials of median digital nerves, median sensory nerve at the wrist, radial sensory nerve at the wrist, and median thenar muscle, all showed progressive reduction in latency, amplitude, duration and area during rising temperature. Our tude, needle electrodes were used for recording, and there was concern that the equivocal results may have been due to inadvertent movement of the tip of the needle during the experiment.5 7 Surface electrodes, although recording lower voltage potentials, remain at an almost constant distance from the nerve, tending to eliminate this source of error. We therefore used surface electrodes in studying the effect of altering limb temperature, within physiological ranges, on the latency, amplitude, duration, and area of the CAP. Antidromic and orthodromic radial sensory conduction studies were performed in 10 healthy subjects. MethodsThe subjects were 23 to 31 years old, six males and four females. In each subject the temperature of the right hand and forearm was lowered by the application of icepacks. All subsequent studies were performed at 15 minute intervals while the limb gradually warmed over approximately two hours. In some subjects, warming was enhanced by the breeze from an electric hair-dryer. Cutaneous surface temperature was monitored at the proximal part of the second digit, centre of the palm and the mid-flexor surface of the forearm immediately after each nerve conduction study.One pair of recording and reference Beckman miniature electrodes were placed 3 cm apart over the superficial radial nerve at the wrist, and a second pair was placed over the median nerve at the wrist. Record-407 by copyright.