In children living in an ecologically unfavorable area the quantitative content of bifidobacteria and enterococci appeared to be considerably decreased while the level of sulfate-reducing clostridia, on the contrary, elevated. The suppression of bifidoflora leads to decreased immune responsiveness that promotes different somatic diseases. Bronchitis, pneumonia, tonsillitis, pharyngitis, otitis, allergic diseases, diseases of digestive organs, acute respiratory virus infections are more often registered in children living in ecologically unfavorable Central district than in children living in the ecologically favorable Lenin district.