 The metabolic syndrome is increasing worldwide, including developing countries. The metabolic syndrome is composed of clinical expressed symptoms as central obesity, high blood pressure, raised fasting plasma glucose or diagnosed diabetes, low HDL, and raised serum triglycerides. All those components together or independently contribute to the development of cardiovascular diseases, which are the leading cause of death in the modern world. The results from previous studies have shown that probiotic bacteria have an influence on health improvement, and can exert positive effects on diseases as diabetes, high blood pressure, dyslipidemia and low-grade inflammation, which are all components of the metabolic syndrome. The objectives of this study were to investigate which of probiotic strains Lactobacillus plantarum PCS 20, Lactobacillus plantarum PCS 26 in Lactobacillus rhamnosus GG exert positive effects in the cascade of molecular reactions at the level of small intestines, at remodeling of monocytesmacrophages and adipocytes in human cell model of non-cancerous origin, and to provide scientific explanation of mechanisms of possible multi-leveled activity of selected probiotic strains in patients with metabolic syndrome. For this purpose, the investigators divided this research into two parts. The first part consisted of pre-clinical in-vitro laboratory study. It examined the mechanisms of actions of probiotic cultures with the use of functional cell models of non-cancerous origin, more specifically, with the use of cell lines of human intestinal epithelium, human monocytesmacrophages and human visceral preadipocytes. In in-vitro laboratory study, the investigators demonstrated that probiotic strain Lactobacillus plantarum PCS 26 exerts positive effects, which could help to relieve the particular components of the syndrome in the host with metabolic syndrome. The second part of the research consisted of prospective, double-blind and placebo-controlled in-vivo pilot clinical study, which included 16 volunteers with the metabolic syndrome. Results have shown that probiotic strain Lactobacillus plantarum PCS 26 exerts positive effects on reduction of waist circumference, on lowering of serum cholesterol concentration, and on maintenance of serum adiponectin levels. Those effects together can contribute to the alleviation of the metabolic syndrome, especially in terms of clinical manifestation and risks in relation to cardiovascular diseases. 