We report the results of a national quality-control survey on glycohemoglobin (GHb), monitored in France by the Société Française de Biologie Clinique on behalf of the authority of the "Agence du Médicament." A sample of lyophilized hemolysate was sent to 3109 laboratories. Results were obtained from 2770 laboratories. HbA1C, HbA1, and total GHb were measured by 50%, 24%, and 26% of the participants, respectively. Of these measurements, 79% of the HbA1C results and 76% of the total GHb results, but only 48% of the HbA1 results, were within the +/- 20% limits of the indicated target values. Mean values for the hemolysate ranged from 8% to 11% for HbA1C, from 7% to 12% for HbA1, and from 11% to 13% for total GHb. The interlaboratory CVs ranged from 3% to 20%, according to method used. So, methods used for GHb assay, which are based on various principles, exhibit very different analytical performances. Nonetheless, this large-scale study indicates that some techniques can support transferability of results from laboratory to laboratory.