A human being has been using lactic acid bacteria in the form of fermented food within living memory, but the history of probiotics is just recent. Several lactic acid bacteria have been recognized as probiotics due to their wide range of health-promoting effects in humans. Their use in the treatment and prevention of a disease, particularly gastrointestinal disease, has yielded many successful results. There is mounting clinical evidence that some probiotics, but not all, help the defence of the host as demonstrated by either a shorter duration of infections or a decrease in the host´s susceptibility to pathogens. The introduction of probiotics to gastrointestinal tract may be a very attractive option to reestablish the microbial equilibrium and prevent disease. This review is focused on the recent findings on the importance of the gut microbiota and on the potential utilisation of probiotics, prebiotics and synbiotics.