• Thirty-two patients with amyotrophic lateral sclerosis were studied with somatosensory evoked potentials (SEPs), visual evoked potentials, and brain-stem auditory evoked potentials. H-reflexes were used to screen for abnormalities of peripheral nerve conduction. Nineteen patients (59%) showed an abnormality of lower extremity SEPs. In 13 patients (40%) the delay was of central origin, while in six patients (19%) peripheral conduction delay was possible. Abnormality of upper limb SEPs was seen in 11 patients (34%), all but two of whom had abnormal lower limb SEPs as well. Four patients (12%) had abnormal brain-stem auditory evoked potentials, all of whom had abnormal SEPs from upper and lower limbs. Four patients had abnormal visual evoked potentials, which in three patients were of minor degree. These results give physiologic evidence to suggest that abnormalities in amyotrophic lateral sclerosis occur outside the motor system.