The invention relates to pharmaceutical compositions comprising different molecules, preferably monoclonal antibodies, each comprising epitopes that bind simultaneously to different sites within the same ErbB receptor domain, preferably the ErbB1 receptor domain. The preferred antibodies according to this invention are MAb 425 and MAb 225 each in its murine, chimeric and humanized version. The invention relates to the use and methods for an improved treatment of preferably tumors by means of said compositions.