Background T cells are among the earliest cells to infiltrate the arterial intima during the initial stages of atherosclerosis. Alterations in the peripheral blood lymphocyte distribution might be associated with intensive lymphocytes extravasation and stimulation of atherosclerotic plaque development. Epidemiological data reveal that short-term postprandial hyperglycemia is a significant risk factor for coronary heart disease. Using a parameter that indicates recently-past acute hyperglycemia, 1,5-anhydro-D-glucitol (1,5-AG), the aim of the present study was to elucidate which alterations in peripheral blood T-lymphocytes, if any, are associated with acute hyperglycemia in patients with type 2 diabetes mellitus (DM) and, thus, might be involved in the progression of atherosclerosis. Methods and Results Measurement of fasting glucose level, glycated hemoglobin A_1c, 1,5-AG, lipid profile and lymphocyte receptors expression (CD3⁺, CD4⁺, CD8⁺, CD8⁺28⁺, CD⁺28 ^-) was performed in 97 patients with type 2 DM, 23 patients with coronary heart disease, and 15 healthy controls. The mean CD3⁺, CD4⁺, CD8⁺28 ^- and CD8⁺28⁺ lymphocyte counts were significantly higher in the DM patients than in both control groups. Multiple regression analysis revealed that CD4⁺ and CD8⁺28^- lymphocyte counts primarily were dependent on 1,5-anhydro-D-glucitol plasma levels. Conclusions These results suggest that acute hyperglycemia results in the progression of atherosclerosis in type 2 DM, at least in part through changes in CD4⁺ and CD8⁺28^- lymphocyte subsets. (Circ J 2007; 71: 962 - 967)