This article examines associations between gluten, polymorphisms of the major histocompatibility complex, and mucosal pathology representative of the spectrum of gluten sensitivity. Sequences of wheat, rye, and barley prolamins contain recurring tetrapeptide motifs that are predicted to have beta-reverse-turn secondary structure and that, with in vitro assays, appear active. Structural polymorphisms of major histocompatibility complex subloci identify codon switches within the second exon that control the third hypervariable region in the outer domain of the beta chain. Observations of the intestinal response to gluten reveal five interrelated lesions (preinfiltrative, infiltrative, hyperplastic, destructive, and hypoplastic) that are interpretable as cell-mediated immunologic responses. These responses originate in the lamina propria, where a series of antigen-specific inflammatory processes has now been identified. There is no evidence that celiac sprue is a disease of jejunal enterocytes. Furthermore, the role of intraepithelial space lymphocytes in pathogenesis, if relevant, needs further experimental dissection. Also awaiting further definition are polymorphisms of the celiac lymphocyte antigen receptor and their relationship to gliadin oligopeptide(s) and predisposing genes. The nature and basis of nonresponsive celiac sprue require more thoughtful initiatives to elucidate the immunologic mechanism(s) of unresponsiveness and evaluate possible means of reversal. Finally, a more sensible definition of gluten sensitivity (unhampered by qualitative morphological imagery) is ultimately called for in order to accommodate the biomolecular advances addressed in this review.