This paper reviews the present notions of the mechanisms of probiotics' action and analyzes selective approaches to correcting the intestinal microflora, such as the use of antibiotic-resistant and highly-adhesive probiotics, treatment with autostrains of lactobacilli and bifidobacteria, and the application of fermented-milk probiotics. Methods for optimization of the intestinal microflora in the newborns by using the maternal strains of bifidobacteria and the drug Zlemik that contains highly-adhesive lactobacilli are discussed. It is shown that parameters of immunotropic activity and involvement in the bacteriocin-mediated interactions may be used to design new probiotics. In future, the application of gene engineering methods will aid in designing a new generation of probiotics with predicted biological properties.