CD30 is a transmembrane cytokine receptor and plays a role in regulating the function, differentiation and/or proliferation of normal lymphoid cells¹. Malignant cells in Hodgkin lymphoma are termed Hodgkin (mono-nuclear) or Reed-Sternberg (multi-nuclear) cells, although they can also be referred to as Hodgkin Reed-Sternberg (HRS) cells. The origin of HRS cells became clear when techniques were established to isolate single HRS cells from biopsy specimens and analyse them for rearranged immunoglobulin genes by single cell PCR. It is now known that these cells represent clonal populations of transformed germinal centre B-cells in both classical Hodgkin lymphoma (CHL) and nodular lymphocyte predominant lymphoma (NLPHL), although in rare cases they can be derived from T-cells. In summary, in CHL, the HRS cells are positive with CD30, often positive with CD15 (in approximately 80% of cases) and generally negative for B-cell antigens such as CD20 or CD79a (approximately 30% of CHL cases will show some staining with these markers). In NLPHL, the HRS cells (also known as L&H cells or popcorn cells) are negative for both CD30 and CD15 and are generally positive for B-cell antigens. CD30 staining is found in CHLs, anaplastic large cell lymphomas, germ cell tumours and in a varying proportion of activated T- and B-cells. The staining pattern of CD30 in CHL is very similar to that of CD15 but without the granulocyte positivity. Some plasma cells will also stain with this antibody