CD30, a single chain glycoprotein, is synthesized as a 90kDa precursor which is processed in the Golgi complex into a membrane-bound phosphorylated mature 105/120kDa glycoprotein. The CD30/Ki-1 antigen is expressed by mononuclear Hodgkin and multinucleated Reed-Sternberg cells in Hodgkin’s disease, by the tumor cells of a majority of anaplastic large cell lymphomas, and by a varying proportion of activated T and B cells. About one third of the Ki-1 positive lymphomas lack the leukocyte common antigen (CD45).