Probiotics are live organisms of the human origin, which after repeated administration, have provable effects on human health. We usually divide probiotics to medicaments with a very detailed documentation of genetics purity, biological behaviour and treatment effectiveness and safety in a certain pathological condition and to probiotics which meet the requirements of dietary supplements, but do not have these detailed data. In the group of probiotic medicaments the best tested microbe is non-pathogenic Escherichie coli, strain Nissle 1917. Probiotics are used in prevention and therapy of diarrhoea induced by antibiotics, in prevention of clostridium colitis origination, in maintenance therapy of ulcerative colitis and in prevention of pouchitis. They have a specific position in the prevention of necrotising enterocolitis origination in newborns.