Colorectal cancer (CRC) is frequently complicated by metastatic disease, with the liver being the most common site of metastasis. Surgical resection is the only realistic cure for colorectal liver metastases; however only 10-25% of cases are initially resectable. The introduction of combination chemotherapy has improved survival rates by enabling 10-20% cases with previously unresectable hepatic metastases to become amenable to surgery. Recent results with the biologic agent bevacizumab, a chimeric human-mouse monoclonal antibody against VEGF, and cetuximab, a chimeric human-mouse monoclonal antibody against EGF receptor, have shown that they improve clinical surgical outcomes when added to current first-line regimens in patients with metastatic colorectal cancer. Dual biologic therapy in combination with chemotherapy has, however, yielded disappointing results. Identification of biological markers is expected to help determine which patients are most likely to respond to these newer agents and thus improve targeted therapy.