The application of highly specific mAbs with minimal side effects in cancer therapy was, for a long time, a major goal for many clinical oncologists. Since their arrival in the clinical setting, mAbs have come to represent a standard therapy for some tumors, and have proven to be an important extension to the treatment of a broad spectrum of malignancies. The future development of mAbs for targeting alone (ie, for labeling of tumors) is insufficient for obtaining a suitable clinical response, and adequate clinical success can only be achieved by arming mAbs and targeting them to functionally significant tumor antigens such as tumor growth-related receptors. This review provides an overview of the functional characteristics of mAbs, together with some important examples of their clinical application. While mAbs may not be the 'magic bullets' that many researchers had hoped for, they are nevertheless becoming an indispensable pillar of tumor therapy.