A retrospective study was conducted to investigate whether the use of low-contrast stimuli in addition to the standard high-contrast stimuli would increase the sensitivity of the pattern-reversal P100 when testing for multiple sclerosis (MS) and optic neuritis (ON). We found that there was a statistically significant increase in the number of abnormal results when using 25' checks, but not for 50' checks. Examination of patient records showed that VEP abnormalities to low-contrast stimuli only was not prognostic for subsequent development of multiple sclerosis.