The development of contemporary knowledge in the field of oral microbiology and probiotics was commenced by Elie Metchnikoff's report on Lactobacillus bulgaricus in 1907. Since then, multiple indications for the use of probiotics have been established, following the WHO definition: "probiotics are live microorganisms, which when applied in adequate amount may benefit the host health status". In accordance with a general classification, several types of bacteria and fungi have been distinguished and, moreover, their mechanisms of action run parallel in both the gut and oral cavity. The possible use of probiotics in dentistry is a relatively new idea. Until now, three species prevailed in available research: Bifidobacterium, Lactobacillus rhamnosus GG and Lactobacillus reuteri. Current research focuses on the application of probiotics and the natural displacement of cariogenic bacteria within the oral cavity, and the subsequent alteration of health status in both adults and children. Carioblis BLIS M18 probiotic, which contains freeze-dried cultures of Streptococcus salivarius M18, was introduced to the market as a supplement indicated for patients with a high caries rate. The aim of this study was to investigate the influence of the BLIS M18 strain on oral cavity microflora and estimate possible health outcomes.