The oral Prausnitz-Küstner (P-K) reaction was examined in 41 children suspected of IgE-mediated food allergy. The recipients were served by their mothers in this study. A positive reaction was observed in 9 children when used hen's egg, cow's milk, chicken, buckwheat, red-bean, salmon or common-dolphin. Among them, seven have had an anaphylactic skin reaction (systemic urticaria and/or angioedema) to the foods. The other two were babies who were fed only by the breast milk. Therefore, the oral P-K test may be useful for the diagnosis and the prediction of food-anaphylaxis. The sera that had the radioallergosorbent test (RAST) scores of 3 or greater were negative in the oral P-K reaction in 26 out of 36 tests, and the sera that showed the positive oral P-K reaction to buckwheat or chicken were zero in the RAST scores. These results suggest that a soluble substance (e.g., histamine-releasing factor) in addition to the IgE antibody might be involved in the oral P-K reaction, and that the RAST technique does not always detect the IgE antibody that recognizes the food antigens degenerated during the absorption in vivo.