We examined the immunohistochemical localization of Glut 1 in sections of developing rat brain [gestational (G) days 18 and 20, postnatal (P) days 1, 10, 21, and greater than 40; term = approximately G21] and characterized the abundance of Glut 1 in isolated brain microvessels by Western blot analysis. Further quantitation of total glucose transporters by [125I]3-iodo-4-azido-phenethyl-amido-7-O-succinyldeacetyl-forskoli n photoaffinity labeling was performed. Glut 1 was prominently distributed in G18 and P1 brain vascular endothelial cells, with comparatively little immunoreactivity observed in brain parenchyma. Conversely, at P10, Glut 1 was prominent in brain parenchyma (undifferentiated cells) and less evident in the vascular endothelium. However, at P21, a resurgence of Glut 1 in vascular endothelial cells was observed, as was a sustained presence in parenchymal cells. On P greater than 40, a distribution in vascular endothelial cells and, to a minor extent, in parenchymal perivascular stellate cells was noted. Microvessel preparation Glut 1 (approximately 55-60 kDa) and [125I] 3-iodo-4-azido-phenethyl-amido-7-O-succinyldeacetyl-forskolin photoaffinity-labeled glucose transporters gradually increased from G18 through P10 to P greater than 40. This developmental increase in Glut 1 was also seen in whole homogenates (approximately 45-47 kDa), but not in crude brain membranes. Thus, isolated microvascular preparations indicated that Glut 1 levels constantly increased with maturation, but direct visualization of brain sections revealed that the localization in different cellular compartments changed with development. These alterations in cellular localization of glucose transporters, appear to occur in concert with the changing glucose metabolic needs of the brain, which, during the various stages of development, exhibits constantly changing phases of cellular growth and proliferation.