Immune globulin (also called immunoglobulin or gamma globulin) is a protein in human blood and tissue fluids. These proteins are similar to antibodies, which help the body's immune system recognize and destroy foreign substances, such as bacteria and viruses.

Immune globulin (IG) may be given to help prevent an illness after exposure to an infected person. It can also be given to people with certain immune system deficiencies to prevent infections. Immune globulin is usually taken from the blood of people recovering from the illness. For example, the immune globulin given to help prevent hepatitis A infection is taken from the blood of people who are recovering from hepatitis A virus infection.

The protection provided by an immune globulin injection lasts from days to months, depending on the disease.