We have investigated the serum level of granulocytecolony stimulating factor (G-CSF) and macrophagecolony stimulating factor (M-CSF) and the commonly accepted tumor markers, such as carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA 19-9) in colorectal cancer. Additionally, we have defined the diagnostic sensitivity, specificity, positive predictive value, negative predictive value and receiver-operating characteristics (ROC) curve for G-CSF and M-CSF. The serum levels of cytokines were measured in 49 patients with colorectal cancer and in 40 healthy subjects. G-CSF and M-CSF were determined using enzyme-linked immunosorbent assay (ELISA). CEA and CA 19-9 were measured by microparticle enzyme immunoassay. There were significant increases in the level of circulating G-CSF and M-CSF in the colorectal cancer patients compared to the control group. Moreover, the diagnostic sensitivity of M-CSF was higher (65%) than the sensitivity of CEA (31%) and CA 19-9 (20%). The diagnostic specificities of M-CSF and G-CSF were 95%, and the M-CSF predictive value was higher compared with the predictive value of G-CSF. These results suggest a potential role for M-CSF as a tumor marker for colorectal cancer.