We examined the effect of intraluminal antigen on intestinal function in an animal model of anaphylaxis using Hooded-Lister rats sensitized to ovalbumin. Older rats were more difficult to sensitize than younger ones; younger rats more consistently developed antiovalbumin titers of greater than or equal to 1:64 as measured by passive cutaneous anaphylaxis. That these immunoglobulins were of the immunoglobulin E class was suggested by the fact that heating of the sera to 56 degrees C for 3 h eliminated the response. Net fluxes of water and electrolytes were measured in sensitized rats with serum titers greater than or equal to 1:64 and compared with nonsensitized sham-treated controls during two periods: when the perfusate was antigen-free and after the addition of antigen. Intraluminal antigen challenge had no effect in controls but caused a rapid and dramatic reduction in water, Na+, Cl-, and K+ absorption in experimental animals (greater than or equal to 1:64). There was no evidence of recovery after antigen withdrawal, and the response was antigen-specific. Mucosal homogenates prepared after antigen challenge in sensitized animals contained significantly less histamine than homogenates prepared from controls, and granulated mucosal mast cell numbers were reduced. Light microscopy did not reveal any alteration of villus height or crypt depth, but mucosal edema was apparent in sections from sensitized animals. The findings suggest that anaphylactic reactions to food proteins in the intestine lead to abnormalities of water and electrolyte absorption and that histamine, or other mast cell mediators, or both, may be responsible.