Probiotic formulations are widely available and have a variety of proposed beneficial effects, including promotion of gut health. The mechanisms of action of probiotic bacteria in the intestine are still unclear but are generally attributed to an antiinflammatory effect. Here, we demonstrate that the multiple probiotic formulation VSL#3 prevents the onset of intestinal inflammation by local stimulation of epithelial innate immune responses (i.e., increased production of epithelial-derived TNF-alpha and restoration of epithelial barrier function in vivo). We also demonstrate that probiotic bacteria stimulate epithelial production of TNF-alpha and activate NF-kappaB in vitro. Our results support the hypothesis that probiotics promote gut health through stimulation, rather than suppression, of the innate immune system. Furthermore, our findings provide the perspective that defects in innate immunity may play a critical role in the pathogenesis and progression of intestinal disorders, such as inflammatory bowel disease.