Background: The presence of hemoglobinopathies could interfere with some assays for Hemoglobin A(1c) (HbA(1c)) measurement; therefore, the effect of thalassemia on ion-exchange high-performance liquid chromatography (IEHPLC) method Tosoh HLC-723 G8 (Tosoh G8) was evaluated. Methods: A total of 43 normal controls and 101 thalassemia patients were quantified by Premier Hb9210 and Tosoh G8 (variant-mode) systems. At the same time, 7 normal controls and 8 thalassemia patients were confirmed by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) reference method for verification. Results: For normal controls, the HbA(1c) values of Tosoh G8 system (y) showed great correlation and agreement with those from Premier Hb9210 (x) (y = 0.9688x + 0.2151, r = 0.9951; mean difference 0.02 +/- 0.30%), and no significant relative bias above 7% was observed; the HbA(1c) values obtained by Tosoh G8 were consistent with the IFCC targets (relative bias < +/- 6%) in all of the samples. However, for thalassemia, the correlation between Tosoh G8 (y) and Premier Hb9210 (x) became relatively low (y = 0.8079x + 1.2897, r = 0.7780); the HbA ie values of 91.1% of the samples (92/101) obtained by Tosoh G8 were higher than those by Premier Hb9210 (mean difference 0.33 +/- 0.48%) and a significant positive bias above 7% was noticed in 43.3% (45/101) thalassemia patients; when compared with the IFCC targets, the 87.5% (7/8) relative bias was > +/- 6%. Conclusions: Thalassemia could directly affect the measurement of HbA(1c) using the IE-HPLC method Tosoh G8 and the clinical laboratorial staff should pay close attention.