We evaluated the changes of the tumor markers CEA and CA19.9 as early predictors of progression in metastatic colorectal cancer (mCRC) patients participating in a clinical study and receiving chemotherapy and bevacizumab (Bev). Seventy-two patients had high baseline CEA or CA19.9 serum levels. By ROC analyses, the areas under the curves were 0.83 for variable CEA cutoff values for distinguishing progressive disease (PD) versus stable disease (SD)/partial remission (PR)/complete remission (CR), and 0.80 for variable CA19.9 cutoff values for distinguishing PD versus SD/PR/CR. Rises in CEA and CA19.9 may early signal the occurrence of progression in mCRC patients receiving chemotherapy and Bev.