Provided is a prophylactic/therapeutic agent for an allergic disease caused by Th2 cell-polarized activation, which comprises at least one kind selected from a branched amino acid, glycine, serine, arginine, a keto acid thereof and a salt thereof. Because the prophylactic/therapeutic agent of the present invention produces almost no side effects, it can be safely ingested routinely and can be taken for a long time. When the prophylactic/therapeutic agent of the present invention is used in combination with an anti-inflammatory drug, the dose of the anti-inflammatory drug can be reduced. Hence, the prophylactic/therapeutic agent of the present invention is useful for the prevention or treatment of an allergic disease caused by Th2 cell-polarized activation. The prophylactic/therapeutic agent of the present invention is particularly effective on bronchial asthma and pulmonary fibrosis that accompanies bronchial asthma.
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