The aetiology of inflammatory bowel disease is still unclean. Whilst a specific pathogen agent associated with these diseases has not been found, the rationale for probiotic therapy in inflammatory bowel disease is based on convincing evidence involving intestinal bacteria in their pathogenesis. Encouraging results have been obtained with probiotic therapy in several animal models of experimental colitis. The administration of highly concentrated probiotic preparations represents a valid approach both for the prevention of pouchitis onset and relapses. The encouraging results obtained in ulcerative colitis and Crohn's disease need to be further assessed in large double-blind trials.