Micromites (genus Dermatophagoides) are the major source of allergens in house dust. Four homologous classes of major allergens have been isolated from extracts of D. pteronyssinus and D. farinae mites. According to current theories, all major mite allergens are proteins of gastrointestinal origin. Group I mite allergens, Der pI and Der fI, are thermolabile glycoproteins with M(r) of 25 kDa. A comparison of primary structure of these proteins reveals a 30% homology with cathepsins B and H, papain and actinidine. Analysis of enzymatic activities reveals that group I allergens are proteolytic enzymes related to the class of cysteine proteinases. With regard to antigenic composition, Der pI and Der fI have three common and two species-specific epitopes. The amino acid sequence of the major allergenic determinant for Der pI has been established. Group II mite allergens, Der pII and Der fII, are single-chain thermostable proteins with M(r) of 10-14 kDa and are said to bear many common features with the lysozyme. Group III mite allergens are analogous to trypsin. A 50% homology of amino acid sequences of Der pIII and Der fIII to those of vertebrate and invertebrate serine proteinases has been found. To the fourth group of major mite allergens one may relate mite amylase (M(r) = 56-60 kDa). A high degree of homology has been established between group IV allergens and mammalian alpha-amylase. Mite allergens of all groups induce the production of specific IgE antibodies in human organism. The use of purified allergens increases the efficiency of diagnosis and treatment of mite-induced allergoses. Modified forms of mite allergens (allergoids, allergens adsorbed on carriers, liposome preparations, etc.) are helpful tools in specific immunotherapy.