The underlying cause of pathology in thalassemia is the premature destruction of red cells, both in the bone marrow and by the reticuloendothelial system. It is generally accepted that the presence of unpaired excess globin chains is the primary circumstance leading to such membrane alterations as oxidation of phospholipids, modification of cytoskeletal proteins and their interactions, reduced membrane-associated ATPase activities, and enhanced permeability of cations. Such perturbations in turn result in the exposure of outer surface neoantigens, enhanced binding of autoantibodies and complement fixation to the outer red cell surface. These factors contribute to the observed distinctive morphologies, increased rigidity and decreased deformability of the thalassemic red cells. In alpha-thalassemic red cells, excess beta-globin chains form homotetramers, Hb H, which are relatively stable and will only damage red cell membrane when precipitated as inclusion bodies, whereas excess alpha-globin chains cannot form such homotetramers and upon synthesis rapidly bind to the cytoplasmic side of the beta-thalassemic red cell membrane, even in young erythroblasts. This difference in properties of the excess globin chains may offer an explanation for the variation in clinical severity observed between these two forms of thalassemia.