This work investigated the function of interneurons and other types of cells in the lateral geniculate nucleus (LGN) in cats raised to adulthood with one eye sutured closed. In order to understand the basis of the commonly found deficit of Y-type relay cells in the deprived layers of the LGN, we looked for reduced or defective activity in other cells which also receive an afferent projection from Y-type ganglion cells in the visually deprived retina. Monocular deprivation did not produce a deficit in the activity of a class of interneurons which receive direct optic inputs from the same ganglion cells in the deprived eye that also drive the Y-type relay cells. Likewise, the Y-type afferent input from the deprived eye to XY-type relay cells was normal. The XY-type cells have mixed or hybrid receptive field properties and both X and Y excitatory inputs; although the Y-inputs to these cells are often much weaker than the X-inputs. The normal properties of Y-type interneurons and XY-type relay cells in the deprived LGN suggest that neither a retinal dysfunction nor an inherent inability of the Y-type optic tract axons to form adequate synapses onto LGN neurons are factors which would readily account for the reduction of Y-type relay cells in monocularly deprived cats. The hypothesis that the deprived Y-type relay cells may have difficulty in forming synaptic connections onto postsynaptic, binocular neurons was supported by observations of responses of cells in the perigeniculate region. Normally, perigeniculate neurons receive a strong binocular input from Y-type relay cells as well as an X-input in at least some cases. In binocular perigeniculate cells of the sutured cats, no inputs from deprived Y-type relay cells could be identified although a longer latency input, typical of that from X-type relay cells, was present.