Summary: Immunoelectrophoresis (IEP) is a method of determining the blood levels of three major immunoglobulins: immunoglobulin M (IgM), immunoglobulin G (IgG), and immunoglobulin A (IgA). It combines electrophoresis and immunodiffusion technique. To run this test, a gel is prepared with alternating wells and slots cut into it. The antigen mixture (usually a serum sample) is placed in the wells and electrophoresis is performed to separate the proteins in the sample. Then an antibody or mixture of antibodies is added to the slots in the gel. The separated antigens and the antibodies migrate toward one another and form precipitin arcs at the region of optimal concentrations.