A human lung squamous cell carcinoma cell line designated KSNY was established from a patient suffering from marked neutrophilia and polyclonal hyper-gamma-globulinemia. In our previous report, we demonstrated colony-stimulating activities in the culture supernatant of this cell line. To determine the exact molecules for the activities, we investigated the gene expression of various cytokines in KSNY cells and showed the mRNA expression of both granulocyte colony-stimulating factor (G-CSF) and interleukin-6 (IL-6). We also detected substantial amounts of G-CSF and IL-6 in the culture supernatant with sensitive enzyme-linked immunosorbent assays (ELISA). The amplification of the gene locus for G-CSF, but not for IL-6 was shown by Southern blot analysis. Furthermore, we also showed that the mRNAs for G-CSF and IL-6 were relatively stable in KSNY cells. These findings are thought to be related to the constitutive production of the cytokines in KSNY cells.