The production of interleukin (IL) 6 from six human liver cell lines, including Chang liver, HLF, HLE, HepG2, PLC/PRF/5, and HuH-7, was investigated using enzyme-linked immunosorbent assay and Northern blot analysis. When cells were cultured in the presence of 12-O-tetradecanoylphorbol-13-acetate, significant amounts of IL6 were detected in the culture supernatants of Chang liver cells, HLF cells, and HLE cells. However, IL6 was not detected in the culture supernatants from HepG2 cells, PLC/PRF/5 cells, or HuH-7 cells which had been treated similarly. To further investigate the production of IL6, expression of the IL6 gene was studied. Results of Northern blot analysis using IL6 complementary DNA as a probe showed that the induction was initiated at the mRNA level. Moreover, IL6 mRNA was also induced by IL1 beta and tumor necrosis factor but not by a calcium ionophore (A23187) or IL6 itself in Chang liver cells. This is the first study to demonstrate the production of human IL6 in liver cells. Furthermore, when the production of alpha-fetoprotein (AFP) from the liver cell lines was examined, the three that were able to produce IL6 failed to produce AFP, whereas the other three cell lines succeeded in producing AFP. These observations may indicate the heterogeneous origin of the liver cell lines.