CEA and CA19.9 are biomarkers routinely measured for monitoring treatment response in metastatic colorectal cancer (MCRC) patients, yet their predictive value during therapies containing new antineoplastic drugs (i.e. FOLFIRI/OLFOX/Bevacizumab) has not yet been investigated. Consecutive chemotherapy-naive MCRC patients treated with either standard chemotherapy-alone (FOLFIRI/FOLFOX) or chemotherapy+bevacizumab (FOLFIRI+bevacizumab) were included in the analysis. Patients had to have serial biweekly measurement of CEA and CA19.9 available for at least three months of treatment. Primary study endpoint was Progression Free Survival (PFS). Biomarker levels and type of treatment as well as major demographic and clinical factors were analyzed for their impact on PFS. Out of 243 evaluated MCRC patients, 87 had biomarkers available as per inclusion criteria. Among all evaluated factors only type of treatment (chemotherapy-alone vs chemotherapy+bevacizumab) and baseline CA19.9 (> vs < normal) were independently associated with PFS, whilst neither baseline CEA nor biomarker reduction during therapy reached statistical significance. When patients with different baseline CA19.9 levels were analysed separately, only patients with abnormal CA19.9 benefited significantly from the administration of bevacizumab.The current study demonstrated a significant predictive value of CA19.9, but not of CEA and biomarker reduction, for MCRC patients treated with new antineoplastic drugs. Moreover, only patients with abnormal baseline CA19.9 levels benefited significantly from bevacizumab.