The responses of neurons in the primary visual cortex (V1) are generally inhibited by stimuli surrounding their classical receptive fields (CRF). This surround suppression can influence the visual perception of stimuli. For instance, the presence of a surround stimulus can decrease the apparent contrast of a central stimulus. A recent neurophysiological study in nonhuman primates suggests that two distinct mechanisms, early and late mechanisms, give rise to surround suppression. Here, we used binocular suppression to render the surround stimuli invisible and evaluated the effects of this masking on the two types of surround suppression. We found that the early mechanism was unsusceptible to, whereas the late mechanism was eliminated by, binocular suppression. The distinct effects of binocular suppression on the early and late mechanisms suggest that the two types of surround suppression arise from different neural substrates.