Since the measurement of HbA1 has become available to the diabetologists, the physicians and patients tend to rely exclusively on this parameter for the assessment of metabolic control. Therefore, in this study, 24 hour glucose profiles of 8 selected patients (4 under intensified conventional therapy, ICT, and 4 under continuous subcutaneous insulin infusion, CSII) with HbA1 values indicating good metabolic control were taken three times at four week intervals and were compared to mean blood glucose (MBG), mean average of glucose excursions (MAGE) and Schlichtkrull's M-value. MBG of the 24 profiles was 114 +/- 21 mg/dl. The patients under CSII were somewhat lower than the patients under ICT. In 16 of the 24 profiles, there was at least one period of hypoglycemia of 50 mg/dl and below. Only in one patient, M-value and MAGE showed stable metabolic control. In conclusion, hyperglycemic excursions in patients under intensified conventional therapy or treated by continuous subcutaneous insulin infusion do escape their reflection in the HbA1 values because of low blood sugar periods following hyperglycemic swings. Undoubtedly, the partial failure of ICT and CSII to prevent diabetic complications might be ascribed to the incomplete assessment of the metabolic control based on HbA1 values exclusively.