More than 50 percent of military personnel developed acute gastroenteritis while on duty in the Gulf. Most of them who reported symptoms of IBS had an acute onset which occurred in association with an episode of acute gastroenteritis during their tour of duty. Other travelers are known to be colonized by new micro-organisms during travel to foreign countries. This acquisition is thought to be related to a change in diet. The natural history of this change in bowel flora, in part, depends on host factors and can persist for months after travel abroad. It seems likely, that PG veterans with persistent diarrhea and a negative work-up for known GI diseases have PI-IBS. No study in the past has evaluated the role of SBBO in causing chronic GI symptoms in PG Veterans. Furthermore, soldiers involved in combat are exposed to a highly stressful environment, perhaps making them more susceptible to persistent symptoms.