S INCE THE INITIAL description of the Ki-l monoclonal antibody (MoAb) in 1982,'there has been an overwhelming flood of information concerning the Hodgkm's disease@)-associated molecule CD30. In a diagnostic point of view, the Ki-l antibody enabled in 1985'the identification of a new category of non-Hodgkn's lymphomas designated as Ki" D30 anaplastic large cell lymphoma (ALCL).' The discovery that the extracellular part of the membrane-bound CD30 antigen is proteolpcally cleaved to produce a soluble form (sCD30) has led to the development of enzymelinked immunosorbent assays (ELISAS) for the detction of sCD30 in the mum of patients with CD30-expressing neoplasms! Recently, through expression screening with anti-CD30 MoAbs,'.'it was possible to clone the gene encoding the CD30 molecule, whereby it was established that CD30 is a new member of the tumor necrosis factor m) receptor superfamdy. 6 This in turn allowed the cloning of the gene encoding the CD30 ligand (CD30L) and its assignation to an emerging family of ligands with homology to TNF.'Finally, the restricted distribution of the CD30 antigen in normal human tissues makes it a potential target for antibody-mediated therapy. This prompted construction of anti-CD30 immunotoxins that have recently been clinically used and shown to display antitumor activity against refractory HD. P All the above developments that span over more than 10 years are extensively discussed in this review.