EPs in response to weak and strong stimuli at 200 points of visual cortex in both hemispheres were recorded in acute experiments on 80 anesthetized cats. Individual and species asymmetry of EP in visual cortex was characterized by its bilateral origin, mosaic localization and time stability. Transection of corpus callosum decreased a slight asymmetry and augmented a strong one. The interaction of endogenous and exogenous asymmetries augments the general asymmetry, particularly with a stimulus in a sagital plane. The data obtained suggest a hemispheric specialization in animals.