The goals of these experiments were to describe the morphology and synapticconnections of amacrine cells in the baboon retina that contain immunoreactivevesicular glutamate transporter 3 (vGluT3). These amacrine cells had themorphology characteristic of knotty bistratified type 1 cells, and theirdendrites formed two plexuses on either side of the center of the innerplexiform layer. The primary dendrites received large synapses from amacrinecells, and the higher-order dendrites were both pre- and postsynaptic to otheramacrine cells. Based on light microscopic immunolabeling results, these includeAII cells and starburst cells, but not the polyaxonal amacrine cellstracer-coupled to ON parasol ganglion cells. The vGluT3 cells received inputfrom ON bipolar cells at ribbon synapses and made synapses onto OFF bipolarcells, including the diffuse DB3a type. Many synapses from vGluT3 cells ontoretinal ganglion cells were observed in both plexuses. At synapses where vGluT3cells were presynaptic, two types of postsynaptic densities were observed; therewere relatively thin ones characteristic of inhibitory synapses and relativelythick ones characteristic of excitatory synapses. In the light microscopicexperiments with Neurobiotin-injected ganglion cells, vGluT3 cells made contactswith midget and parasol ganglion cells, including both ON and OFF types. Punctacontaining immunoreactive gephyrin, an inhibitory synapse marker, were found atappositions between vGluT3 cells and each of the four types of labeled ganglioncells. The vGluT3 cells did not have detectable levels of immunoreactiveγ-aminobutyric acid (GABA) or immunoreactive glycine transporter 1.Thus, the vGluT3 cells would be expected to have ON responses to light and makesynapses onto neurons in both the ON and the OFF pathways. Taken with previousresults, these findings suggest that vGluT3 cells release glycine at some oftheir output synapses and glutamate at others.