Rates of dehydroascorbate uptake by blood granulocytes and mononuclear cells are slower, and plasma ascorbate concentrations are lower, among persons with diabetes mellitus than in nondiabetic subjects. These measurements do not correlate with one another or with simultaneously measured plasma glucose or glycosylated hemoglobin; they do not differ with type of diabetes or mode of treatment. In those diabetic granulocytes that exhibit slow dehydroascorbate uptake, maximal velocity (Vmax) transport rates for dehydroascorbate, 2-deoxyglucose, and 3-O-methylglucose are decreased, each to the same degree, while Km values for transport of these ligands are not different from those observed in nondiabetic cells. Since diffusion of these ligands is facilitated by a common transporter, these observations may reflect decreased numbers of glucose transporters in the plasma membranes of some diabetic leukocytes.