The author estimated the effects of GH or Atonin-ACTH administration on the transaminase activity in the rat brain and liver. The activities determined were aspartate-glutamate (AsGT), alanine-glutamate (AlGT), and γ-aminobutyrate-glutamate (γAGT) transaminases. The GH administration was found noneffective on the transaminase activities of the brain and liver of the normal rat. When GH was administered to the hypophysectomized rat, the previously increased activites of the AsGH and γAGT in the brain and liver decreased to the normal values. By the administration of Atonin-ACTH, the AsGT activities of the brain and liver increased in the case of the normal rat, and decreased in the case of the hypophysectomized rat.