Summary: Probiotics are living microorganisms that provide the body with health benefits. They have great potential for preventive or therapeutic actions in various gastrointestinal disorders, but the mechanisms responsible for the effects of action have not yet been fully elucidated. Probiotics are involved in the inhibition of diarrhea, e.g. in lactose intolerance, they have antimicrobial activity, can alleviate symptoms in inflammatory diseases of the intestines or in irritable bowel syndrome. Although not all preparations have proven their efficacy in clinical trials, modulation of the gut microbiota with probiotics provides interesting possibilities of prophylaxis and treatment.