We have used the fluorescent dye Rhodamine-B-Isothiocyanate (RITC) as an anterograde and retrograde marker of retinal neurons in the adult rat. Introduced into the vitreous body, RITC is taken up by retinal ganglion cells and transported anterogradely along their axons. It labels the axons and their terminal arborizations. The dye stains axonal projections for at least 30 days without detectable extracellular leakage or transneuronal passage. Furthermore, the soma and dendrites of retinal ganglion cells can also be labeled retrogradely for at least 30 days when RITC is instilled into the superior colliculus. We conclude that RITC, used previously in studies of chick embryo visual pathways, is also suitable for similar neuroanatomical investigations in the adult rat.