 Determine the safety and efficacy of different doses of VSL3 in the treatment of children with irritable bowel syndrome: Children will be recruited from the pediatric gastroenterology clinic at The Childrens Medical Center in Dayton, Ohio. Eighty four children will be enrolled in this controlled, double-blinded, randomized study. All children will have had a prior evaluation by a pediatric gastroenterologist who has diagnosed these patients with irritable bowel syndrome and excluded organic disease as a cause of the childs abdominal pain. 