Microbiological study of pharyngeal mucosa in 43 children with solid tumors revealed that 77.2% of isolated microorganisms belonged to Gram-positive flora. It was shown that streptococci and Staphylococcus aureus were the main species. Species composition of streptococci included both pyogenic (S. pyogenes, S. agalactiae, S. dysgalactiae, S. equi) andviridans species (S. acidominimus, S. oralis and "S. milleri" group). Nocardioform actinomycetes, corynebacteria and other staphylococci were referred to additional microflora. Accidental microflora was represented by Neisseria spp., non-fermenting Gram-negative bacteria, enterobacteria and yeast-like fungi. Microbiologic study of pharyngeal mucosa biocenosis showed that monoculture was present only in 2.3% of cases; in other cases microorganisms formed both intra-genus and inter-species associations. 2-6-component associations were revealed with predominance of 3-4-component associations (37.2% and 32.6% respectively). Relationship of distribution of microorganisms belonging to main and additional microflora was revealed.