Hypersensitivity to environmental allergens has increased in the last years. Several authors have described the physicochemical properties, nucleotide and amino acid sequences, and also the three-dimensional structure of unknown allergens. The aim is to identify T- and B-cell epitopes and to understand the regulatory mechanism of the excessive immune response. The induction of specific IgE antibody production in genetically predisposed subjects is the characteristic allergens have in common. New molecular biological studies indicate that, especially in monosensitized subjects, a correlation exists between the HLA-D system and the allergen-specific IgE immune response.