A special group of substances that are very dangerous for the biosphere includes war gases such as mustard gas (bis(2-chloroethyl)sulphide). The influence of mustard gas hydrolysis products (MGHPs) on soil microbiota has been investigated. These substances bear numerous toxic effects on soil microorganisms. They change significantly the number and the specific composition of soil microbiota and inhibit the enzyme activity of soils. The main "ecological targets" of mustard and its hydrolysis products' toxic action have been determined. MGHPs affect the growth and reproduction of soil micromycetes, as well as their morphological and cultural properties. Increase in number and size of mitochondria in the fungal cells is accompanied by increase in dehydrogenases activity. Cell permeability influenced by MGHPs grows in connection with concentration of toxicants. Increase of permeability corresponds to growth of the amount of unsaturated fatty acids. The changes in the fatty acid composition of lipids in the cells of the soil micromycetes display their adaptation to adverse impact of the substances studied. MGHPs and thiodiglycol enhance synthesis of polysaccharides and pigments.