A molecule that has been formed by attachment to each of two originally different molecules. One of these is an antibody and, hence, the word “immunoconjugate.” Classic organic drug molecules such as methotrexate, adriamycin chlorambucil, etc.; radionucHdes; enzymes; toxins; and ribosome-inhibiting proteins may be conjugated to antibodies. The salient point is that the antibody portion of the conjugate is there to “steer” the biologically active molecule to its target.