Evoked potentials were recorded in three different visual experiments in 14 patients with amyotrophic lateral sclerosis (ALS) and 14 matched control subjects. Control subjects' evoked potentials (EPs) were characterized by an initial positivity in the 90-140 ms range (P1) at the temporo-occipital site. This component was absent from the group average of the ALS patients as well as the individual patients' EPs. As the P1 is known to emanate from inferior occipito-temporal areas, this finding provides electrophysiological evidence for a cortical involvement in ALS including visual areas.