The technique that we use for pattern shift visual evoked response (PSVER) is described. PSVER is a non-invasive, practical and reliable clinical test in detecting anterior visual pathways lesions even when asymptomatic. The ability to find unsuspected lesions in multiple sclerosis, making possible an early diagnosis, is underscored. We also discuss some pathophysiologic aspects and the findings of the PSVER in some neurologic disorders with visual system involvement.