Rationale: Clinical trials have demonstrated that probiotics may be effective in the treatment and prevention of atopic disease in children but there have been few reports of therapeutic effects of oral probiotics outside the gastrointestinal tract. Objectives: We investigated the effect of two probiotic organisms on the response to antigen challenge in a mouse model of allergic airway inflammation. Methods: We utilized an ovalbumin sensitized asthma model in Balb/c and Toll-like receptor 9 deficient mice. Animals were treated with probiotic organisms via gavaging needle prior to antigen challenge. Following antigen challenge, airway responsiveness to methacholine, influx of inflammatory cells to the lung and cytokine levels in bronchoalveolar lavage fluid was assessed. Results: Oral treatment with live Lactobacillus reuteri but not Lactobacillus salivarius significantly attenuated the influx of eosinophils to the airway lumen and parenchyma and reduced the levels of TNF, MCP-1, IL-5 and IL-13 in bronchoalveolar lavage fluid of antigen challenged animals but there was no change in eotaxin or IL-10. L.reuteri but not L.salivarius also decreased allergen-induced airway hyperresponsiveness. These responses were dependent on Toll-like receptor 9 and associated with increased activity of indoleamine 2,3-dioxygenase. Killed organisms did not mimic the ability of the live L. reuteri to attenuate inflammation or airway hyper-responsiveness. Conclusion: Oral treatment with live L.reuteri can attenuate major characteristics of an asthmatic response in a mouse model of allergic airway inflammation. These results suggest that oral treatment with specific live probiotic strains may have therapeutic potential in the treatment of allergic airway disease.