Characteristic features of fauces aerobic microflora in children treated in intensive care units (ICU) were analysed. For comparison fauces microflora in children outpatients and in children patients from general surgical units was investigated. A retrospective analysis of all the smears without exception for 2 years (a total of 2120) revealed a direct dependence of the changes in the fauces microflora composition on the patient condition and the antibiotic load. It was shown that the fauces indigenic microflora in ICU patients was more often replaced by enterococci, gramnegative enteric bacteria and nonfermenting bacteria which are not usual under the normal conditions. The flora in such cases was represented by monoculture. Thus, microorganisms natural for the fauces i.e. Haemophilus influenzae and Neisseria spp. were not practically detected in the fauces of the ICU patients (0.5 and 0.4 per cent, respectively). Grampositive cocci in the children of the surgical units and in the outpatients included alpha-hemolytic streptococci in association with beta-hemolytic or nonhemolytic streptococci. No such bacteria were isolated from the ICU newborns. The associations of gramnegative organisms from the ICU patients included 40 variants. Seventy-eight association variants of Pseudomonas aeruginosa were mainly represented by the combinations with Serratia spp. and Klebsiella spp. as well as with coagulase negative staphylococci or enterococci, especially in the ICU newborns. The results of the study demonstrated that the target-aimed antibiotic therapy providing eradication of P.aeruginosa in the ICU patients was not always justified because of possible superinfection practically due to any organism from the association. Massive antibiotic therapy with pressing on gramnegative flora in the ICU patients induced selective contamination of the mucosa by polyresistant enterococci thus increasing their potential role in the development of hospital infections.