The possible involvement of the corpus callosum in binocular functions of the visual cortex was studied in adult cats. Unit recording was made in areas 17, 18 boundary following posterior or complete transection of the corpus callosum, acutely as well as chronically, after short (3-4 months) and long (5.5-39 months) survival periods. A considerable reduction of binocularly driven cells was found in the posteriorly callosally transected cats (acute: 41% cells; short-chronic: 65%; long-chronic: 32%). Similar results, albeit smaller in the long-survival group, were found following complete callosal transection. In comparison, the proportion of binocular cells in the normal cats was 85%. It was concluded that the corpus callosum is involved in interhemispheric integration and enhancement of binocularity in visual cortex cells. No recovery occurs as function of time following cancellation of the interhemispheric interaction by callosal transection.