Monoclonal antibodies are a new class of agents targeting at specific receptors on cancer cells. In addition to having direct cellular effects, antibodies can cany substances, such as radioactive isotopes, toxins and antineoplastic agents, to the targeted cells. Two of them, cetuximab (Erbitux) and bevacizumab (Avastin), seem to have acquired a significant role in the management of patients with radically resected and advanced colorectal carcinoma. Cetuximab plus irinotecan has been approved as second-line therapy in irinotecan-resistant colorectal cancer patients; bevacizumab plus 5FU/LV has resulted in higher response and longer survival than 5FU/LV alone in first line metastatic colorectal cancer; its combination with oxaliplatin has recently doubled results. The superior therapeutic efficacy of these molecular targeting agents over traditional chemotherapy has been shown by the survival benefit achieved by patients with advanced or recurrent cancers. Although the precise molecular mechanism by which these agents produce or enhance an antitumour effect, alone or in combination with anticancer drugs, is unknown, the specific inhibition of target genes critically involved in tumour progression and metastasis is clear. Further studies to determine which patient groups and anticancer drugs are more appropriate for combination therapy with these agents are needed. All the most important data obtained through recent studies are discussed, emphasizing their mechanisms of action, safety profiles and clinical applications.