Hodgkin disease (HD) is characterized by the presence of a small number (usually <1% of total tumor mass) of the typical Hodgkin and Reed-Sternberg (H-RS) cells in a hyperplastic background of normal reactive lymphocytes, plasma cells, histiocytes, neutrophils, eosinophils, and stromal cells. HRS cells produce various cytokines, growth factors, and express cytokine receptors and activation antigens, implying a predominant role for these molecules in the pathophysiology of Hodgkin disease. HD may therefore be regarded as a tumor of cytokine producing cells. The CD30 antigen has been characterized as a marker for cultured and primary Hodgkin and Reed-Sternberg cells, and was found to be overexpressed in Hodgkin disease and a subgroup of non-Hodgkin lymphomas including large cell anaplastic lymphomas and Burkitt lymphomas. The molecular cloning of the CD30 antigen revealed that CD30 is a member of the tumor necrosis factor/nerve growth factor receptor superfamily. The cloning of the cognate for CD30, currently termed CD30 ligand, confirmed that the CD30 antigen functions as a cytokine receptor. Recombinant CD30 ligand is a membrane-bound protein with pleiotropic biological activities for different CD30+ lymphoma types, but also for the immune system, mainly T cells. CD30L belongs to the emerging tumor necrosis factor ligand superfamily. The CD30-CD30 ligand interaction could have a critical pathophysiological role in malignant lymphomas, particularly Hodgkin disease, large cell anaplastic lymphomas and Burkitt lymphomas, and is also involved in activation and functioning of the T cell-dependent immune system.