IgE (Immunoglobulin E) is a glycoprotein with a molecular size of 190 kDa composed of 2 light chains and 2 heave chains (H ). In electrophoresis, it moves to γ1 region. Its biological half life is about 3 days, and its blood level in normal human subject is very low, about 300 ng/ml. The blood level of IgE increases markedly in parasite infection and in hay fever. IgE that is responsible for allergy has been called “reagin”. Sensitization by an allergen increases reagin IgE which binds to FcεR1 receptor in basophilic leucocytes and mast cells at Fc region and sensitizes those cells. If the allergen binds the sensitized cells, those cells will be degranulated and release histamin, serotonin, protease, heparin, chemotactic factor, prostaglandins, leucotriens, and so on, causing bronchoconstriction, mucous edema, and hypersecretion, and leads to type I allergic reactions like bronchial asthma, hives, allergic rhinitis, anaphylaxis, and so on. This is the assay kit for total mouse IgE. Shibayagi is also providing assay kits for allergen(OVA)-specific mouse IgE.