It was shown previously that bee-collected pollen (bee pollen, BP), inhibited in vitro murine mast cell activation. This study further analysed the antiallergic effect of BP in vivo by measuring cutaneous mast cell activation using a passive cutaneous anaphylaxis reaction. Daily oral administration of BP to mice, dose-dependently reduced the cutaneous mast cell activation elicited by IgE and specific antigens. Administration of BP also reduced the plasma concentration of malondialdehyde (MDA), an indicator of lipid peroxidation. The inhibitory effect of BP was mostly in a lipid- but not in water-soluble fraction. The HPLC analysis of isoflavones in BP revealed that genistein was a major isoflavone. However, administration of genistein alone at the concentration found in BP, did not show an inhibitory effect as observed in whole BP, suggesting that component(s) other than genistein would be responsible for the inhibitory effect of BP. These results first reveal that lipid-soluble components of BP exert an antiallergic action by inhibiting the FcåRI-mediated cutaneous mast cell activation.