AbstractThe retinal ganglion cells projecting to the superior colliculus (SC) and dorsal lateral geniculate nucleus (LGNd) of the North American opossum(Didelphis virginiana)were studied by using the horseradish peroxidase (HRP). The four ganglion cell size groups recognized previously were found to project in systenatically different ways. After injections of HRP into the superior colliculus, labeled cells were seen in nasal retina contralateral to the injection and in temporal retina both ipsilateral anc contralateral to the injection. In contralateral nasal retina cells of all size classes were labeled, while in contralateeral temporal retina small (8–14 μm diameter), small‐medium small‐medium (15–19 μm diameter), and large (>24 μm diameter)cells were labeled but few, if any, large‐medium (20–24 μm diameter)cells were labeled. In ipsilateral temporal retina, soma size groups labeled included small‐medium, large‐medium, and large cells, but very few small cells. A nasal–temporal difference in the soma size of ganglion cells projecting to the SC was found: Labeled cells in temporal retina were 1.7–4.2 μm larger than their counterpats in nasal retina.Following injection of HRP into the LGNd, label was seen in contralateral nasal and ipsilateral temporal retina witn no label seen in contralateral temporal retina. The labeled cells were small‐medium, large‐medium, and large. No small ganglion cells were labeled from the LGNd. A small nasal‐temporal soma size difference in retinal ganglion cells projecting to the LGNd was seen: labeled cells in temporal retina were 1.0–2.1 μm larger than in nasal. It is concluded that all four ganglion cell size groups in the opossum project to the SC, but that only the