Crohn's disease has a high morbidity and there is no known cure. Current treatments have multiple side effects and an effective treatment with minimal side effects is desired. Probiotics have been proposed as such a treatment but their efficacy is undetermined. There is some evidence that probiotics are effective in other conditions affecting the gastrointestinal tract and they are popular with patients. They are thought to work through competitive action with commensal and pathogenic flora, influencing the immune response.