Quantitative autoradiography was used to determine the topographical and time patterns of L-[3H]glutamate and D-[3H]aspartate high-affinity uptake system in the hippocampal formation of the rat during postnatal development. Extended control experiments were performed to verify the specificity of labelling. For short incubation periods of 3-10 min, the data demonstrated a conspicuously low rate of glutamate accumulation in the hippocampal formation of newborn animals and a marked increase in labelling of hippocampal neuropil areas during the first weeks of postnatal life. Our autoradiographic data on developmental increase in glutamate high-affinity uptake levels are consistent, in terms of time and topography, in many ways with other parameters of maturation of glutamatergic and/or aspartatergic structures in the hippocampal formation.