A clinical bacteriological examination was applied to 100 newborns with intestinal infections caused by opportunistic gram-negative aerobes. There was a correlation between the decrease in the quantity of the bifidobacteria and the predominance of various species of opportunistic gram-negative aerobes and their associations, as well as high sensitivity of clinical isolates of the opportunistic bacteria to phosphocin, gentamicin, polymyxin and specific bacteriophages. The study showed that the combined use of antibiotics with the biopreparations (the specific bacteriophages and bifidumbacterin) was effective in treating the newborns with the above mentioned infections.