IgG, IgA and IgM levels were studied in 187 homozygous β-thalassemic patients and compared with age-matched normal control subjects. The not yet transfused and the polytransfused nonsplenectomized patients showed a significant increase of all Ig classes. The polytransfused splenectomized patients showed a significant increase only of IgG and IgA. The splenectomized patients, when compared to the nonsplenectomized ones, showed a significant increase of IgG, of IgA in the elder ones and a significant reduction of IgM. High ASLO and ASFLO titers were found especially in the splenectomized patients. The high Ig levels in younger not yet transfused patients, with little iron storage and normal hepatic enzyme values, demonstrate that transfusion therapy and liver damage do not play a main role in hypergammaglobulinemia. The absence of antimitochondrial, anticonnective tissue and homogeneous antinuclear antibodies seems to exclude a deficient suppressor mechanism. The hemocatheteric ‘overworking’ of RES may reduce the antigen clearance with a consequent increase of antibody response. Splenectomy, by removing a consistent part of RES, enhances the phenom