The increased level of HbA2 is a reliable marker of heterozygous beta-thalassaemia. The levels of HbA2 measured by three different methods were compared and the ranges for the normal and for the heterozygous beta-thalassaemia were assessed. The levels of HbA2 2.76 +/- 0.47% for normal (30 blood donors) and 4.62 +/- 0.77% for beta-thalassaemia (50 patients) were obtained by the chromatographic method 2.61 +/- 0.42% HbA2 for normal (30 blood donors) and 5.82 +/- 0.89% HbA2 for beta-thalassaemia (46 patients) were assessed by electrophoresis on hydragel (Sebia) and 2.8 +/- 0.62% HbA2 for normal (30 blood donors) and 6.04 +/- 0.96% HbA2 (47 patients) were found when using cellulose acetate electrophoresis. An increased level of foetal Hb was found in nine patients with beta-thalassaemia. The diagnosis of beta-thalassaemia was confirmed by molecular genetic methods in all cases with an elevated HbA2 level, while a normal HbA2 level did not rule out heterozygous beta-thalassaemia.