Travelers to developing countries often develop diarrhea, which is usually caused by consuming food or water contaminated with bacteria. Daily antibiotics can prevent travelers' diarrhea but have many adverse effects, such as making bacteria in the body more resistant to antibiotics. Therefore, the risk of taking daily antibiotics to prevent travelers' diarrhea is usually considered greater than the benefit. Rifaximin, an antibiotic used in other countries to treat diarrhea, recently became available in the United States. Rifaximin is an effective treatment for travelers' diarrhea once it has developed and might also be useful for preventing travelers' diarrhea.