Specificity of folate conjugates for the FR has been shown by competition tests with free folate. When this ligand, known to bind the FR, is added in excess of the folate conjugate, it outcompetes the conjugate, indicating that the folate conjugate specifically binds the FR, and not other receptors, in the process of receptor-mediated endocytosis. Addition of an enzyme that frees the folate receptor from the cell membrane and addition of antibodies to the FR also reverse the internalization of folate conjugates, providing further evidence that folate conjugates bind the FR with specificity.[1]