Single cells were recorded in layers A and A1 of the cat dorsal lateral geniculate nucleus (dLGN) with multibarrel micropipettes. Interocular inhibition ("binocular inhibition") was elicited by phase-reversing gratings presented monocularly to the nondominant eye. This inhibition was blocked by microiontophoretic application of bicuculline and thus proven to be GABAergic. Cortical cooling enhanced the inhibition from the nondominant eye. After localized destruction of the receptive field area in the dominant eye, duration and strength of discharge depression were increased. It is concluded that afferent activity from the dominant eye reduces inhibition from the nondominant eye in the dLGN.