Immunoglobulins (antibodies) are proteins that circulate in the blood. They provide protection from diseases by binding to foreign proteins (for instance the proteins that are present on infectious viruses or bacteria), inhibiting activity and forming large complexes which are rapidly cleared from the circulation. There are 2 broad types of immunoglobulin preparations, "normal" and "specific".

Human Normal Immunoglobulin preparations are used in the treatment of patients who have no, or very low levels of, antibody production. This may be due to a genetic disorder, to disease, or to treatment such as chemotherapy.  They are also used in the treatment of certain auto-immune conditions.

Specific immunoglobulins are preparations that contain a high concentration of antibodies to particular viruses or bacteria. If these products are given soon after exposure to the virus or bacterium concerned (e.g. soon after being bitten by a rabid animal), they will help to fight infection. This is particularly important in cases where the affected person has not previously been vaccinated against the virus or bacterium. In such cases it takes several days before the patient's own immune system produces effective antibodies.