Six patients with unilateral epiretinal membrane of the macula perceived the spontaneous Pulfrich psychophysical stereo-illusion, suggesting a relative conduction delay on the side of the membrane. In three of these patients, visual-evoked potential studies were also obtained and confirmed an absolute conduction delay in the anterior pathway on the side of the epiretinal membrane in two patients and an absence of the P 100 wave on the side of the epiretinal membrane in the third patient. It is important to recognize that the Pulfrich psychophysical stereo-illusion can be spontaneously perceived in macula disease, and therefore, the test may not always distinguish optic nerve from macula disease.