We have investigated the serum level of granulocyte-colony stimulating factor (G-CSF) and macrophagecolony stimulating factor (M-CSF) in non-small-cell lung cancer (NSCLC), in relation to the control group and commonly accepted tumor markers, such as carcinoembryonic antigen (CEA) and cytokeratin fragment 19 (CYFRA 21-1). Additionally, we have defined the diagnostic sensitivity, specificity, positive predictive value, negative predictive value and receiver-operating characteristics (ROC) curve of G-CSF and M-CSF. Serum levels of cytokines were measured in 61 patients with NSCLC and in 20 healthy subjects. G-CSF and M-CSF were determined using ELISA. CYFRA 21-1 was measured by radioimmunoassay and CEA by microparticle enzyme immunoassay. There were significant increases in the level of circulating G-CSF in the lung cancer patients compared to the control group. Moreover, the diagnostic sensitivity of G-CSF was higher (56%) than the sensitivity of CYFRA 21-1 (51%), but lower than the CEA sensitivity (62%). The diagnostic specificity of G-CSF was higher (70%) than the M-CSF specificity (40%) and the G-CSF predictive values were higher in relation to the predictive values of M-CSF. These results suggest a potential role of G-CSF as a tumor marker for NSCLC.