Tropomyosin had been identified as a major allergen in shrimp. The digestion and absorption of tropomyosin (Pen j 1) from kuruma prawn were investigated by ex vivo, in vitro, and in vivo techniques in order to elucidate the relationship between the allergenicity of the allergen and its gastrointestinal behavior. Pen j 1 transported the Caco-2 monolayer in a dose-dependent manner, and also enhanced the permeability of lucifer yellow, a marker of paracellular transportation, at high concentrations of the allergen. Studies with everted sacs revealed that Pen j 1 was rapidly degraded to small peptides (MW<3.5 kDa) and amino acids by intestinal proteases and absorbed from enterocytes. Furthermore, Pen j 1 orally administered to rats tended to remain in the stomach rather than in the small intestine, after which the allergen moved to the epithelial cells. These observations suggest that Pen j 1 may be absorbed via the gastric mucosa prior to its digestion in the intestines.