Human gut microbiota, complex ecosystem of microbes associated with human gut, is essential for the development of the host's immune system and many other physiological functions. Recently, numerous diseases and syndromes were associated with disruption of this ecosystem thus stressing its importance in maintaining the host's health. Growing evidence suggests that by manipulating the gut microbiota, some of these diseases could be treated or even prevented. These manipulations include changes in diet, use of probiotics, prebiotics, antibiotics and fecal microbiota transplantation (FMT). The successes in FMT treatment of recurrent infection of Clostridium difficile led recently to a great interest in extending this treatment modality to other diseases with proven disruption of gut microbiota, such as ulcerative colitis or metabolic syndrome. Key words: Clostridium difficile - dysbiosis - fecal microbial transplantation - microbiota - prebiotics - probiotics.