Food protein-induced enterocolitis syndrome (FPIES) is a non-IgE-mediated gastrointestinal food allergy which is considered to be mediated by allergen-specific T cells. Cow's milk FPIES patients have been reported to show a proliferation of either Th2 cells or IL-9-producing T cells according to the lymphocyte proliferation test using cow's milk allergens. Further studies to clarify whether these allergen-specific T cells in the peripheral bloods are involved in the pathogenesis of FPIES are needed. Although some of the patients have specific IgEs to the allergens, the role of humoral immunity remains unclear. Intestinal mast cells might play a role as effector cells in FPIES, and therefore the factors associated with the induction or activation of intestinal mast cells should be investigated.