SINCE 1947, when Dawson1 described a method which made it possible to record somatosensory evoked cortical potentials from the human scalp by means of a computeraveraging technique, there has been considerable interest in the broader applications of these methods. Recent studies by Bickford and associates2 have focused attention on the occurrence of evoked motor responses in association with the more classical potentials of cortical origin. Widespread myogenic responses, below movement threshold, to sound and to photic stimulation have been described and have been named the "sonomotor response" and the "photomotor response," respectively. The contaminating effect that these potentials can have on evoked responses recorded from the scalp and the difficulties of their separation have already been stressed. This report describes the myogenic potentials resulting from median nerve stimulation and illustrates how these responses also may contaminate scalp-recorded somatosensory evoked responses.3 In addition, studies undertaken to