In the last four years we established five long term cultures from tumor material of Hodgkin's disease. The in vitro cells have malignant characteristics and represent the in vivo H- and SR-cells. Common immunological, functional and morphological assays did not characterize the in vitro cells to be a known cell type of lymphoid, myeloid or monocytoid tissue. The in vitro Hodgkin cells are biologically active by producing factors involved in regulation and promotion of immunological response and granulopoiesis. The relevance of the findings for pathogenesis and clinical appearance of Hodgkin's disease is discussed.