Abstract: There is increasing evidence supporting the involvement of immune cells and mediators in the control of intestinal physiology. Cell coculture systems and epithelial cell lines have provided convenient model systems for the study of immunomodulation of epithelial function. Abundant cytokines and immune mediators have been shown to directly or indirectly alter epithelial transport of ions and macromolecules. Animal models of hypersensitivity have shown that luminal antigen challenge in the intestine of sensitized rats induces a rapid ion secretory response due to enhanced transepithelial transport of antigen. Transport of ions and macromolecules is highly regulated and an important component of host defense. Dysregulation of epithelial function may play a role in several intestinal disorders, such as inflammatory bowel diseases and food allergy.