In 43 insuline dependent diabetics postprandial serum glucose concentrations as 24-hour glucose excretions have been determined. Their value for a long term metabolic information was compared to that of HbAIc concentrations. A correlation between postprandial serum glucose concentration of the partial correlations. Those excluded the influence of an interrelationship among the individual serum glucose concentrations, at the time of different presentations for metabolic control, on the serum glucose to HbAIc relationship. There was no correlation between the concentrations of HbAIc and the amount of glucose excreted into the urine. The study shows that single determinations of postprandial serum glucose concentrations, as the excretion of small amounts of glucose into the urine are of no use for a long term metabolic information in juvenile diabetics.