The content of taurine and the immunocytochemical localization of taurine and γ-aminobutyric acid (GABA) in the rat retina during postnatal development are described. The rat retina is immature at birth; about two-thirds of the cells are undifferentiated neuroblasts, and the taurine content per retina is approximately one-seventh of the adult value. Shortly after weaning the adult morphology and taurine content are attained. Expression of taurine immunoreactivity (taurine-IR) accompanies differentiation; in some cell types (ganglion and horizontal cells) this expression is transient, while in others (photoreceptors, bipolar, and a subpopulation of amacrine cells) it persists into the adult state. At birth, taurine-IR is localized mainly in cells in the position of ganglion cells, especially in their axons within the nerve fiber layer. This reactivity is soon lost from the somata, and disappears from the axons by 10 days of age. At 2 days of age, taurine-IR appeared additionally in somata of amacrine cells flanking the forerunner of the inner plexiform layer, and in growth cone-like processes of photoreceptors. At day 6, taurine-IR was marked in photoreceptor cell inner and outer segments, and in horizontal cells and their lateral processes. Taurine-IR was lost from horizontal cells and most amacrine cells around day 10, and appeared in bipolar cells, where it remained, with that in photoreceptors, into adulthood. Particularly striking was taurine-IR in large synaptic terminal-like processes close to the ganglion cell layer which were first seen around day 16. GABA immunoreactivity was never seen in photoreceptor or bipolar cells, was expressed transiently in horizontal cells at the same time as taurine-IR, but persisted in a subpopulation of amacrine cells and synaptic lamina in the inner plexiform layer and in some fine glial processes in the adult.