We successfully established a human gastric cancer cell line, HuGC-OOHIRA, from the ascites of a 60-year-old patient with advanced gastric cancer (poorly differentiated adenocarcinoma) complicated by peritonitis carcinomatosa and leukocytosis of unknown origin. Morphologically, the cells were polygonal and adhered weakly to the culture flask. They tended to pile up upon reaching confluence. Chromosome analysis revealed that the cell line has two modes of chromosome number, namely near diploidy and tetraploidy. Double minutes (DMs) were present in abundance in each cell. The doubling time was 25-30 hr. The cell line was successfully transplanted into nude mice, and their peripheral leukocyte counts increased in proportion to the growth of the tumors. At 2 weeks after the transplantation, the serum rG-CSF level was elevated to 2,893 pg/ml. The concentration of human G-CSF in the culture supernatants was an extraordinary high level of 145,380 pg/ml/day. Secretion of GM-CSF and IL-6 was also detected. The intracellular localization of the G-CSF was identified for the first time by immunofluorescence. Moreover, Northern blot analysis detected G-CSF mRNA in this cell line. Anti-recombinant human G-CSF serum suppressed the propagation of HuGC-OOHIRA cell line. Therefore, it is likely that the autocrine growth loop by G-CSF is present in this cell line. This cell line would be very useful for understanding both the cellular and molecular basis for the production of various cytokines such as G-CSF as well as cytokine-dependent tumor proliferation.