During the last decade the traditional view of epithelial function being controlled solely by the endocrine and nervous systems has been expanded by the realization that immune cells also have an important part to play in the control of intestinal physiology. Here, we review the current immunophysiological data pertaining to the control of the function of the intestinal epithelium, with particular reference to ion secretion. The role of immunocompetent cells (lymphocytes, mast cells, and granulated phagocytes) and their chemical messenger molecules (ie, biogenic amines, eicosanoids, cytokines) is discussed and the general theme of cell cooperation and integration is emphasized.