The concentrations of glucose transporter in the cerebral cortex and brainstem of neonatal (4-7 days old) and adult rats were measured using [3H]cytochalasin B binding. There was significantly lower binding in neonatal cortex (1.9 +/- 0.7 pmol/mg protein) compared to adult (8.9 +/- 2.5 pmol/mg protein). Scatchard analysis indicates this difference is due to a lower Bmax (neonate, 9.7 pmol/mg protein; adult, 18.6 +/- 1.3 pmol/mg protein). Measurement of [3H]cytochalasin B binding in microvessels prepared from cortex of adult (28.1 +/- 3.5 pmol/mg protein) and neonate (12.8 +/- 1.9 pmol/mg protein) indicates a lower binding in the microvasculature of neonates, whereas no such difference was seen in the binding in microvessels prepared from adult and neonatal brainstem (adult, 11.8 +/- 2.3 pmol/mg protein; neonate, 9.4 +/- 2.7 pmol/mg protein). In both adult and neonate brain, there is an enrichment of glucose transporters in the microvasculature.