Glycated hemoglobin can be assayed by methods using different principles, whose performances vary and are difficult to control. The most widely used techniques measure either specifically glycated A1c hemoglobin (HbA1c) or total glycated hemoglobin. They are reviewed in detail in this paper and standardization problems due to the absence of reference materials and methods are discussed. HbA1c seems to be considered the most significant parameter for monitoring diabetic control. Standardization of the assays, calibrated with reference to this parameter, could be performed provided there is strict control of the methods performance.