It is now well accepted that the vertebrate retina contains on the order of 50-60 distinct neural cell types. Why does the retina, situated at the earliest stage of the visual process, require so many cell types? One hypothesis is that the photoreceptor responses to light are channelled into a number of parallel signal pathways that separately encode various aspects of a visual image and play different roles in visual perception. In the retina each of these visual pathways would be composed of a set of interneurons linked to an output neuron, the ganglion cell, whose axon projects to a target in the brain. To test this hypothesis we are attempting to identify each of the retinal ganglion cell types and their associated interneurons. Work in the lab has recently focused on the retina of the human and macaque monkey. In the primate we know that some ganglion cell types receive excitatory input from red, green, or blue cone photoreceptors and therefore show color selective light responses; other ganglion cell types are excited equally by all of the cone types and are non-color selective. The neural organization that gives rise to these distinct signal pathways is unknown. To approach the problem we are using intracellular recording and staining in in vitro preparation of the macaque retina to identify the color-coding light responses of morphologically identified ganglion cell types.