EVOKED cortical potentials can be recorded through scalp electrodes from human subjects by the application of averaging computer techniques. The method has been employed by several investigators, 1-5 and the findings are in substantial agreement. It is apparent, however, that the amplitude and configuration of the evoked potentials can be affected by several factors. 2,6 To provide a base line for the evaluation of evoked somatosensory potentials in patients with neurological disease, we have studied these responses in 20 individuals with normal neurological findings. Methods Most of the examinations were conducted in a room shielded with copper wire screen, but some were carried out on the ward or in the operating room. Disk stimulating electrodes are placed over the median nerve using the palmaris longus tendon as a landmark. The distal electrode is always negative and is located at the flexion crease of the wrist, while the positive electrode