A chromatographic method utilizing a carboxymethylated poly(vinyl alcohol) resin for a more accurate determination of stable haemoglobin A1c (St-A1c) has been developed. The complete separation between St-A1c, labile HbA1c (L-A1c) and HbF was achieved by gradient elution with sodium chloride in phosphate buffer. This high resolution permits accurate quantitation of St-A1c, even in the presence of high levels of HbF or L-A1c. In 142 subjects with normal fasting plasma glucose and normal response to a 75-g oral glucose tolerance test, the reference interval of St-A1c was 2.80-3.98%.