FIELD: medicine. SUBSTANCE: method involves determining the most characteristic symptoms of chronic fatigue syndrome and carrying out bacteriological examination of feces for its intestinal flora state twice or thrice during the treatment course on the background of a complex of conventional biochemical and immunological tests. Stable lack of bifidum bacteria growth of 10-7 being observed with lactobacteria growth being not greater than 10-6 and Escherichia coli contents being not higher than 50-100 mln/g, chronic poisoning as a result of unbalanced intestinal microflora is diagnosed. EFFECT: enhanced accuracy of diagnosis. 1 tbl
