In an attempt to evaluate binocular functions in an objective manner, visual evoked responses (VER) were recorded in sixteen subjects, six with normal binocular functions and ten with various degrees of squint and binocular impairment. The two eyes were stimulated monocularly or dioptically with a polaroid checker board pattern viewed through rotating polaroid discs. The rate of pattern reversal was 7 per sec for one eye and 10 per sec for the other, allowing stimulus locked responses to be recorded from each eye individually, even during dioptic viewing. In normal subjects the VER of each eye to binocular stimulation were reduced to half or less of the monocular value. The reduction was much smaller in humans with impaired binocular vision, at least for the dominant eye. In stereoblind subjects the response of the dominant eye was the same for monocular and binocular stimulation. The VER changes might reflect binocular interaction in visual cortex neurons, which probably are binocular in normal subjects but driven only from one eye in stereoblind subjects.