GLUT1 is the primary glucose transport protein in human red blood cells (RBCs) but also transports oxidized vitamin C (dehydroascorbic acid; DHA). A recent study suggests that RBC GLUT1 transports DHA as its primary substrate and that only a subpopulation of GLUT1 transports sugars. This conclusion is based on measurements of cellular glucose and DHA equilibrium spaces rather than steady-state transport rates. We have characterized RBC transport of DHA and 3-O-methylglucose (3-OMG; a transported, non metabolizable sugar). Steady-state 3-OMG and DHA uptake in the absence of intracellular substrate are characterized by similar Vmax (0.16 ± 0.01 and 0.13 ± 0.02 mmol/L/min respectively) and K_m(app) (1.4 ± 0.2 and 1.6 ± 0.7 mM respectively). 3-OMG and DHA compete for uptake with K_i(app) of 0.7 ± 0.4 mM and 1.1 ± 0.1 mM respectively. Uptake measurements using RBC inside-out-membrane vesicles (IOVs) demonstrate that 3-OMG and DHA compete at the cytoplasmic surface of the membrane with K_i(app) of 0.7 ± 0.1 and 0.6 ± 0.1 mM respectively. Intracellular 3-OMG stimulates unidirectional uptake of 3-OMG and DHA. These findings indicate that DHA and 3-OMG bind at mutually exclusive sites at both exo- and endofacial surfaces of GLUT1 and are transported via the same GLUT1 complex.