IgE (immunoglobulin E) is the 5th immunoglobulin found and is composed of 2 heavy chains which contain 5 domains (VH, CH 1–4) and 2 light chains. It is a glycoprotein with molecular weight of 190kDa, and in electrophoresis it moves to 1 region. Metabolic half life of IgE is about 3 days in man, and normal serum level in human is about 300 ng/ml, however, it is markedly increased in parasite infection and hay fever. Allergy-related IgE is called reagin. The Fc region of reagin increased after sensitization with allergens will bind Fc R1 receptor of basophilic granulocytes and mast cells in the skin, respiratory, and digestive organs, and sensitizes those cells. Those IgE-sensitized cells will be degranulated when the second allergens bind the surface IgE, and release histamine, serotonine, protease, heparin, chemotactic factors, prostaglandins, leucotriens, etc., causing type I allergy reactions. Shibayagi’s OVA-IgE ELISA KIT is a useful tool for studying mouse immune system by measuring specific anti-OVA IgE after immunization of mice with OVA (ovalbumin).