Immunoglobulin replacement therapy in the form of intravenous immunoglobulin (IVIgG) is clearly of benefit in primary hypogammaglobulinaemia and related disorders involving antibody deficiency. However, its use in the prevention of infection in other conditions is controversial and needs to be clarified. IVIgG therapy may be of benefit in selected patients with IgG subclass deficiency, and with a proven history of recurrent upper respiratory tract infections. IVIgG therapy may also benefit infants with AIDS and recurrent bacterial infections, but is only rarely of value in cases of adult AIDS. The use of 'normal' IVIgG from unselected blood donors to treat viral infections, infections due to gram negative organisms, or to neutralise endotoxin, is probably not indicated on theoretical and practical grounds, and because of the high cost. IVIgG preparations derived from plasma donations selected for high specific antibody levels to the relevant microorganism will probably be of greater benefit than normal IVIgG in patients with specific infections.