We determined erythrocyte concentration of phosphorylated glycolytic intermediates and adenosine nucleotides in 9 non-ketotic diabetics under different conditions of glycemic control. We showed a significant increase of G6P, F6P and FDP levels in the 9 diabetics with poor glycemic control, whereas other phosphorylated glycolytic intermediates were in the normal range. After achieving fair glycemic control G6P, F6P and FDP fell to normal value. G6P, F6P and FDP were well correlated with simultaneously determined plasma glucose. Another 5 diabetics with poor glycemic control were connected to Biostator in order to determine the time relationship between blood glucose and erythrocyte levels of G6P, F6P and FDP. We demonstrated a prompt decrease to the normal values of the phosphorylated glycolytic intermediates where blood glucose fell to normal 60-90 minutes after automatic insulin delivery. Finally, we determined RBC glycolytic intermediates in 5 subjects with normal OGTT and in 5 subjects with normal fasting plasma glucose but abnormal OGTT. In this group we observed a prompt and persistent increase of G6P, F6P and FDP levels over the three hours hyperglycemia phase which has been induced by glucose load. No significant increase was found in subjects with normal OGTT. Our results demonstrate that erythrocyte glycolytic metabolism in abnormal in diabetics, depending strictly on the degree of glycemic control.