We recently found that dietary raffinose suppressed allergic airway eosinophilia in ovalbumin-sensitized Brown Norway rats. Using this model in the present study, we compared the efficacy of other oligosaccharides with that of raffinose. Brown Norway rats were immunized s.c. with ovalbumin on d 0 and exposed to aerosolized ovalbumin on d 20; broncho-alveolar lavage fluid was obtained on d 21. In Expt. 1, rats were fed a control diet or diets supplemented with different oligosaccharides (50 g/kg diet, raffinose, alpha-linked galactooligosaccharide, fructooligosaccharide, and xylooligosaccharide). The number of eosinophils in the fluid was significantly lower in rats fed raffinose and alpha-linked galactooligosaccharide diets than in those fed the control diet. Dietary fructooligosaccharide and xylooligosaccharide did not affect airway eosinophilia. In Expt. 2, i.p. administration of raffinose and alpha-linked galactooligosaccharide, but not fructooligosaccharide and xylooligosaccharide, suppressed airway eosinophilia in rats fed the control diet. In Expt. 3, suppression of airway eosinophilia by dietary alpha-linked galactooligosaccharide occurred in cecectomized rats administered neomycin. Reduced levels of interleukin (IL)-4 and IL-5 mRNA in lung tissue were associated with the suppression of airway eosinophilia. We propose that indigestible oligosaccharides differ in their suppressive effect on allergic airway eosinophilia in ovalbumin-sensitized Brown Norway rats and that the effect appears not to be mediated by intestinal microflora.