Intestinal bacteria play a key role in inflammatory bowel disease. Probiotics attempt to modify disease by favourably altering bacterial composition, immune status, and inflammation. Until recently, probiotic therapy was considered 'folk' medicine, but there now is emerging interest on the part of the general public and scientific communities in the use of probiotics in human disease. This practical, evidence-based review examines probiotics as therapy for inflammatory bowel disease in humans. There are very few such published randomized clinical trials, but some data exist that possibly show an efficacy of probiotics as maintenance therapy in chronic relapsing pouchitis. Obstacles to providing probiotic therapy include selection of appropriate strains, poorly regulated probiotic quality standardization, processing and human biologic factors which impair probiotic viability, difficulty in maintaining new bacterial populations in the gut, and local product unavailability. Studies have focused on specific inflammatory bowel disease subgroups, limiting general applicability for the practitioner. Basic research highlights the importance of bacteria in these conditions, and the possibility that probiotics will modify physiological parameters. Well-designed, randomized clinical studies are still required to define the role of probiotics as therapeutic agents in inflammatory bowel disease.