The essential role of glycohemoglobin measurements in diabetes care and the currently poor comparability of results between different methods used in clinical laboratories makes an international standardization absolutely necessary. The IFCC working group on HbA1c standardization is going to develop a reference system for the international standardization which is based on HbA1c as the biochemically well-defined major glycohemoglobin component, and consisting of primary and secondary reference materials, a reference method and adjusted reference and target values. The system will serve for the standardization of all glycohemoglobin assays.