A method of identifying a combination of antibodies with a combined improved anti-tumor activity is provided. The method comprising: (a) identifying binding epitopes of anti ErbB-2 antibodies; and (b) selecting a combination of at least two antibodies of the anti ErbB-2 antibodies exhibiting binding to different epitopes on the ErbB-2, at least one of the different epitopes being localized to a dimerization site of the ErbB-2, the combination of antibodies being with the combined improved anti-tumor activity. Also provided are novel antibody combinations uncovered according to the present teachings.