One approach to increase specificity of action was to attach drugs or toxins to anti-cancer antibodies.This resulted in drug-antibody conjugates and immunotoxins.Another approach was to find the correct monoclonal antibodies, some of which have become efficient drugs for cancer, like antibodies to epidermal growth factor receptor (EGFR or ErbB1) and to ErbB2.Later on we observed a significant synergistic effect when a small chemotherapeutic drug was given simultaneously with an antibody against EGFR, namely, cetuximab (erbitux), an observation which has by now been used in the clinic (1).More recently, we investigated the strong synergistic effect when the antibodies against the same receptor are used together, provided they are against epitopes sufficiently distant from each other.This was found for EGFR (2), as well as for ErbB2 (3).The advantage for such combination of drugs (or therapeutic vaccines) will be discussed.