This chapter deals with selected aspects of high-performance liquid chromatography (HPLC) methods for quantitating of glycohemoglobin (HbA1C) and characterizing some Hb variants. Determination of HbA1C by ion exchange HPLC is used for monitoring of glycemic control in diabetic patients. The percentage of HbA1C reflects blood glucose concentrations of the previous 2-3 months. It is therefore considered a valuable indicator of long-term diabetic control [1]. However, the methods currently used for its measurement in clinical chemistry laboratories show large differences between reported values, and comparison of results from different laboratories is difficult [2], Lack of standardization of glycohemoglobin measurements remains the major source of interlaboratory variation. At present there is no acknowledged reference method or an accepted standard. This fact is well recognized and an IFCC (International Federation of Clinical Chemistry) working group is developing a reference method based on HbA1C as the biochemically well-defined major glycohemoglobin component. Recently, the use of calibration based on a cation exchange HPLC method has been shown to increase the comparability between various analytical methods [3,4].