Disclosed is a means that can be used for modifying a biologically or pharmacologically active substance from a form incapable of permeating the blood-brain barrier to a form capable of permeating the blood-brain barrier. Also disclosed is a modified substance obtained by using the means. The means is anti-human transferrin receptor antibody and the modified substance is a molecular conjugate of a biologically active protein or a pharmacologically active low-molecular-weight compound and anti-human transferrin receptor antibody.揭示可用於將具有生理活性或藥理活性且無法通過血腦障壁的物質改變成能通過血腦障壁的形態的手段、以及此手段所致之改變物質。該手段為抗人類運鐵蛋白受體抗體，該改變物質為生理活性蛋白質或藥理活性低分子化合物、與抗人類運鐵蛋白受體抗體之分子的結合體。
