CD30, a transmembrane single-chain glycoprotein with a molecular weight of 120 kDa, is the receptor for the cytokine ligand CD30L, which plays an important role in lymphocyte activation, and is expressed in activated T/B cells, R-S cells, and cells around some lymphoid folliclesm. Anti-CD30 detects a formalin-resistant epitope that is expressed by Reed-Sternberg cells in classic Hodgkin lymphoma, the majority of anaplastic large cell lymphomas, primary cutaneous CD30 positive T-cell lymphoproliferative disorders,^1-3 and in embryonal carcinomas.⁴ Occasionally diffuse large B-cell lymphoma stains with this antibody.³ This antibody also stains plasma cells in paraffin-embedded tissue as well as reactive immunoblasts. The staining pattern of anti-CD30 in lymphoma and embryonal carcinoma is different, with the former being membranous and exhibiting Golgi zone accentuation in location, and the latter being membranous only.⁴