Interleukin 6 (IL-6) is a pleiotropic lymphokine which can stimulate a variety of cells including B and T lymphocytes. It has been suggested that IL-6 plays a crucial role in several diseases such as human plasmacytoma, cardiac myxoma or Castleman's Disease by autocrine or paracrine stimulation. To analyse whether IL-6 is involved in the biology of Hodgkin's Disease (HD), we investigated the expression of IL-6 and IL-6 receptor (IL-6R) in cell lines and primary specimens from patients with HD. IL-6 specific transcripts were detected in three out of six HD derived cell lines by Northern blot analysis and in the culture supernatants of four HD derived cell lines by ELISA. Its biological activity was confirmed by proliferation of an IL-6 dependent cell line. By in-situ hybridization experiments IL-6 specific transcripts were detected in Hodgkin (H) and Reed-Sternberg (RS) cells in primary tissues in two out of three patients. mRNAs specific for the IL-6 receptor were detected in five HD derived cell lines. Staining of HD derived cell lines revealed expression of the receptor molecules in five cell lines; Western blot experiments confirmed the 80kDa receptor protein in the cells. Immunohistology in primary specimens revealed expression of the receptor molecules on H and RS cells in 8 out of 16 cases with HD. Expression was mostly detected in the mixed cellularity subtype of HD. Elevated levels of IL-6 were detected in the sera of more than 50% of patients with HD. Taken together our data suggest that IL-6 might be involved in the biology of HD.