ABSTRACT. This review discusses experimental and clinical evidence for the existence of immunologically mediated damage to the intestinal mucosa. The discussion of mechanisms of gastrointestinal immunoregulation and lymphocyte recirculation via recently described homing receptors is preceded by a summary of the basic structures of the gut-associated lymphoid tissues (GALT). The relevance of food-induced systemic hyporesponsiveness (oral tolerance) to the prevention of immunologically mediated damage to intestinal mucosa is discussed in the light of anaphylactic (Type I) and delayed type (Type IV) hypersensitivity reactions. Other, less well defined, mechanisms of allergic injury are also briefly discussed. It is postulated that the abrogation and/or modulation of orally induced tolerance is the pathogenetic mechanism underlying the induction of food-sensitive enteropathies.