The effect of blood transfusions on the immune response of 46 thalassaemic children was studied. Cell-mediated immune response was evaluated by performing skin tests to specific (streptokinase-streptodornase and candidin) and nonspecific (dinitrochlorobenzene and phytohaemagglutinin) antigens. Antibody response to a specific antigen (tetanus toxoid) was estimated by measuring the tetanus antitoxin titre before and after vaccination. No gross impairment of cell-mediated immunity was elicited. The larger proportion of negative phytohaemagglutinin skin tests found in thalassaemic patients does not necessarily suggest a cell-mediated immunity impairment, since this skin reaction is also affected by other factors, especially the inflammatory skin response. The transfused antibodies may inhibit the recipient’s sensitization and primary immune response to the homologous antigen, especially when the antibody level in the transfused blood is high, whereas the secondary immune response is not affected.