Background: The gastrointestinal mucosa is an important route of entry for microbial pathogens. The immune cells of Peyer's patch (PP) compartments contribute to the active immune response against infection. Although local anesthetics are widely used in clinical practice, it remains unclear whether local anesthetics such as lidocaine affect PP T cell functions. Methods: The aim of this study was to examine if lidocaine has any effects on mouse PP T cell functions. To test this, freshly isolated mouse Peyer's patch T cells were incubated with lidocaine. The effects of lidocaine on concanavalin A-stimulated PP T cell proliferation and cytokine production were assessed. The effect of lidocaine on PP T cell mitogen-activated protein kinase (MAPK) activation was also assessed. Results: The results indicate that lidocaine suppresses cell proliferation, cytokine production, and MAPK activation in PP T cells. Furthermore, we found that the chronic in vivo exposure to lidocaine increases bacterial accumulation in PP. Conclusion: The enhanced immunosuppressive effects of lidocaine on PP T cell functions could contribute to the host's enhanced susceptibility to infection. © 2011 Mosby, Inc. All rights reserved.