Means that can be used to modify a substance that has physiological activity or pharmacological activity and cannot pass through the blood-brain barrier into a form that can pass through the blood-brain barrier, and a modified substance thereby are disclosed. The means is an anti-human transferrin receptor antibody, and the modifying substance is a molecular conjugate of a physiologically active protein or a pharmacologically active low molecular weight compound and an anti-human transferrin receptor antibody.生理活性又は薬理活性を有し血液脳関門を通過できない物質を血液脳関門通過可能な形態に改変するために用い得る手段，及びこれによる改変物質が開示されている。当該手段は，抗ヒトトランスフェリン受容体抗体であり，当該改変物質は，生理活性蛋白質又は薬理活性低分子化合物と抗ヒトトランスフェリン受容体抗体との，分子的結合体である。
