The detection of hidden visual loss is important in establishing the diagnosis of multiple sclerosis, especially in patients who have neurologic symptoms of the disease. Both visual evoked potentials and contrast sensitivity have been used for this purpose. We compared the sensitivities of pattern-reversal visual evoked potentials and contrast sensitivity, measured with the Vistech VCTS 6500 chart, in detecting hidden visual loss in 18 patients with multiple sclerosis whose visual acuity was correctable to 20/20 (6/6) or better in the examined eye. Thirteen patients had delayed visual evoked potential latencies. An additional four patients had reduced P100 amplitudes without prolonged latencies. Nine patients had abnormal contrast sensitivity. The visual evoked potential was more sensitive than contrast sensitivity at detecting hidden visual loss in patients with multiple sclerosis (p less than 0.01).