Increased haemoglobin (Hb) A2 levels associated with reduced mean corpuscular volume (MCV) and Hb content per cell (MCH) are the most typical features of heterozygous beta thalassaemia. However, double heterozygotes for alpha and beta thalassaemia may have normal MCV and MCH but Hb A2 always in the carrier range. In this report we describe two Sardinian families who have increased Hb A2 levels, normal red blood cell indices and normal globin chain synthesis and in whom DNA sequence analysis of beta and delta globin genes did not reveal any abnormality. Our findings demonstrate the existence of a genetic trait not resulting from a defect of the beta globin gene cluster, transmitted in a dominant manner and manifested as isolated increase of Hb A2.