Letters to the Editor Dear Sirs, The ABO blood group, the most important among human blood group systems, consists of complex carbohydrate moieties at the extracellular surface of red blood cell (RBC) membrane (1, 2). Along with their expression on RBCs, ABO antigens (namely, A, B, AB and O) are also highly expressed by a large number of human cells and tissues, including epithelia, sensory neurons, platelets and the vascular endothelia (3, 4). It seems thus biologically plausible that the ABO system may expand its clinical significance beyond the traditional boundaries of immunohaematology, transfusion and transplantation medicine. There is growing evidence from the scientific literature that the ABO blood group system may be actively involved in the pathogenesis of a number of human disorders, including cardiovascular, infectious, neoplastic and other diseases (5-8). The fact that ABO blood type may be associated with human disease and may impact on morbidity and death is another intriguing matter of debate, which has stimulated the interest of several investigators over the past 50 years (9, 10). In particular, recent data are supporting the existence of a positive relationship with cardiovascular disorders (11). A particularly interesting model to assess whether the ABO blood groups may contribute or not to promote life extension by eluding most serious diseases is the investigation of the blood