Intramuscular Immunoglobulin (IMIG) have been used for 40 years in substitution therapy for antibody deficiencies and as prophylaxis for and treatment of several infectious diseases. Modified and intact intravenous immunoglobulin preparations (IVIG) have now been available for more than 10 years: only the intact product express full Fc- mediated functions with a biological half-life of IgG (3-4 weeks). These preparations have constituted an important achievement in the treatment of humoral immunodeficiencies also resulting in a dramatic improvement of the prognosis. The use of IVIG has also modified the therapeutic approach to several secondary and acquired immunodeficiencies. Treatment with IVIG for immune modulation in several diseases is investigated: substantial data indicate a useful role in selected cases of idiopathic thrombocytopenic purpura, Kawasaky disease and in some neurologic diseases. IVIG are substantially safe and severe side effects have been rarely reported.