Stable glycosylated hemoglobin measurement provides an index for plasma glucose control over an average three month period. It is not clear whether stable HbA1C can undergo rapid changes induced by short-term variations in glucose concentration. The present study was aimed at investigating whether variation of total HbA1C in response to changes in blood glucose, over a short period can be detected by routine methods of determination. Our result show that due to the sensitivity of the methods, stable HbA1C has to be considered only as an index of glucose control over long period of time.