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. Ber-H2 distinguishes large cell lymphomas derived from activated lymphoid cells from histiocytic malignancies and lymphomas derived from resting and precursor lymphoid cells or from anaplastic carcinomas. About one third of the Ki-1 positive lymphomas lack the leukocyte common antigen (CD45).