The tumour cells of a human cholangiocarcinoma cell line, HuCC-T1, were found to express mRNA of interleukin-6 (IL-6) and to secrete a large amount of biologically active IL-6 in the culture medium at the concentration of 22.6 ng/mL. Interleukin-6 was demonstrated in the cytoplasm of the cells by immunohistochemical staining. Furthermore, these cells showed the presence of receptors for IL-6 on the surface, and DNA synthesis of the cells was stimulated by the exogenous addition of recombinant human IL-6 into the culture medium. The cell growth was significantly inhibited in the presence of anti-human IL-6 antibody in the culture medium. These findings indicate that IL-6 is one of the autocrine growth factors of this cell line in vitro.