Intravenous immunoglobulin (IVIg) are therapeutic preparations of intact IgG that are obtained from a pool of more than one thousand healthy blood donors and contain antibodies directed toward a large panel of microbial agents. IVIg contain high amounts of antibodies with opsonising activity and are indicated in substitutive treatment of patients with constitutive hypogammaglobulinemia. IVIg also contain antibodies able to neutralize certain bacterial toxins exerting superantigenic activity, and by this mechanism exert both anti-infectious and immunomodulating activity. During the last fifteen years, indications of IVIg in the prophylactic treatment of infections have been well defined: a) primary antibody deficiency; b) multiple myeloma and chronic lymphocytic leukemia with hypogammaglobulinemia and recurrent bacterial infections; c) bone marrow allograft; d) childhood AIDS; e) chicken pox seroprophylaxis in immunosuppressed patients and pregnant women. Therapeutic indications of IVIg in infectious diseases are limited to chronic parvovirus B19 infection associated or not with HIV infection. Other therapeutic indications are not well defined.