Probiotic bacteria, commensals selected for their presumed therapeutic properties when ingested orally, have attracted increasing attention for their possible efficacy in a range of gastrointestinal disorders, including the inflammatory bowel diseases of Crohn's disease and ulcerative colitis. Since the barrier properties of the intestinal epithelium are believed to be compromised as a consequence (or perhaps as a cause) of intestinal inflammation, we hypothesized that probiotics might ameliorate such epithelial dysfunction as part of their spectrum of beneficial effects. We have used both cell line and animal models to test this hypothesis and show that two probiotics have significant effects on epithelial barrier properties, both at baseline and when deranged by inflammatory cytokines or in the setting of inflammation in a mouse model of colitis. Moreover, the probiotics also normalize epithelial ion transport function, which could also contribute to clinical efficacy. Overall, our studies extend the spectrum of functional effects attributable to probiotics, and may provide a rationale for their use in a range of gastrointestinal disorders associated with epithelial dysfunction.