Visual evoked potential (VEP) latency to a sinusoidal grating pattern was measured in each eye of 103 patients with multiple sclerosis (MS) and compared with results in a control group of 56 patients hospitalized for other neurological conditions. Of the 50 patients classified as having definite MS, 90% showed prolonged latency (over 131 msec) in one or both eyes. In each eye of 24 of the MS patients, psychophysical measurement of the detectability of grating patterns was obtained. This test was abnormal in 11 of 13 patients with definite MS, 3 of 4 with probable MS, and 5 of 7 with possible MS. There was no concordance between prolonged VEP latency and visual impairment as revealed by the psychophysical test. Apparently pathways determining VEP latency and spatial contrast detection may be unequally affected in MS.