Serum IgG, IgM, IgA, IgG subclasses (IgG1, G2, G3, G4), isohemagglutinins and complement-3 concentrations were measured in 23 beta-thalassemic patients suffering from recurrent infections. No significant abnormalities were found in these humoral immunity investigations, both in splenectomized and non-splenectomized patients. On the other hand, iron overload or repeated blood transfusions were not found to down-regulate the humoral immune system of thalassemic patients.