A chromatographic method for determining glycated hemoglobin (Hb A1c) by use of a new monodisperse cation-exchanger has been investigated. Hb A1c was separated from other "minor hemoglobins": Hb F, Hb A3 (the glutathione adduct), and the acetaldehyde adduct in alcoholics. The method was fully automated and a single column could be used for more than 1000 runs. The normal reference interval was 4.0-5.2%; the interval for diabetic outpatients was 5.6-12.4%. Within-run and the between-run CVs were less than 0.9% and 1.7%, respectively. Carbamylation in uremic patients who were undergoing hemodialysis increased the proportion of Hb A1c to 1%. Hb A1c results were compared with results from glucose tolerance tests. In our study, Hb A1c less than 5.5% excluded diabetes: subjects with Hb A1c greater than 6.2% showed diabetes. If blood sampled during fasting had been screened with determinations of glucose and Hb A1c, only 20% of referred subjects would have needed an oral glucose tolerance test for diagnosis of diabetes.