1. Survey of the pertinent literature leads us to believe that the small bowel is intimately involved in the production of symptoms in gastro-intestinal food hypersensitivity. 2. A roentgenographic approach is described, whereby changes in the small intestine in sensitive and nonsensitive patients may be evaluated under controlled conditions. 3. In a group of 12 patients with clinical gastrointestinal food hypersensitivity, roentgenographic abnormalities of the small intestine, consisting of narrowing, segmentation and scattering, were found following the feeding of a specific barium-allergen mixture. The absence of similar significant changes in the barium-water control studies, made on the same patients, and in both the barium-water and barium-food series in non-sensitive patients indicates the importance of these findings. 4. Abnormalities of the small intestine could not be demonstrated in food hypersensitive patients whose allergic disturbances were not manifested in the gastrointestinal tract. 5. It is worthy of emphasis that the changes described in the small bowel are, in themselves, non-specific and acquire diagnostic significance only when a comparable study without the allergen, made on the same patient after a sufficiently long elimination of the suspected food, is normal.