A technique has been devised for isolating biodestroyer micromycetes from Works of art. As a result of the investigation of damage to old Russian fresco painting and works of applied art it has been established that in order to isolate the significant species, it is necessary to use media whose composition must correspond with the object damaged in addition to the standard media and the specific conditions of the development of biodestroyers in museums. It is proposed that determination should be made of the degree of pathogenesis for museum objects of microscopic fungi, isolated from them, in accordance with their formation of extracellular hydrolytic enzymes, organic acids, pigments and physiological peculiarities, such as their adaptation to the low activity of water, and to antiseptics used in the museum practice, and others.