Two new diagnostic tools to assess blood glucose control in ambulatory diabetics have recently been introduced. The first represents a self-monitoring of ambient blood glucose levels by the patient who prepares capillary blood samples during a day of regular activities. Blood glucose is determined by the laboratory on the following day. Self-monitoring of 24 hr blood glucose profiles is valuable to assess blood glucose excursions, and particularly, to detect unrecognized hypoglycemias. The second new tool is the determination of hemoglobin A1 or A1c which represents an indicator of blood glucose control during the last 3-4 months. We noted in stable non insulindependent diabetics a highly significant correlation between fasting blood glucose levels and hemoglobin A1c content. Since in these patients there is also a close correlation between fasting blood glucose and average daily blood glucose levels, a correlation was calculated between the mean daily blood glucose level and HbA1c content. Derived from this correlation, the average daily blood glucose level can be estimated from the HbA1c value in insulin-dependent diabetics in whom the casual blood glucose may not be representative for their overall blood glucose control. Thus HbA1 resp. HbA1c represents a reflection of the mean blood glucose level during the last 3-4 months. Particularly, it allows the detection of metabolic decompensation which is not clinically evident and which remained undiscovered by single blood glucose measurements.