A new kinetic analysis of blood-brain glucose transport is described, based on a steady-state model that takes account of cerebral blood flow, mean capillary glucose concentration, and cerebral metabolic rate. The maximal rate (Tmax) and half-saturation constant (Km) of glucose transport from blood to brain were determined in rats by measuring the rate of blood-to-brain glucose transfer at different blood glucose concentrations. Each determination lasted 20 seconds. For whole-brain, Tmax and Km averaged 258 +/- 33 (S.E.) mumol L(100 g)-1 min-1 and 5.9 +/- 1.6 (S.E.) mmol 1-1, respectively. The regional variations were insignificant. The new approach permits kinetic parameters to be measured locally in brain in rapidly changing functional states.