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 follicles. Anti-CD30 detects a formalin-resistant epitope expressed by Reed-Sternberg cells in classical Hodgkin’s lymphoma, the majority of anaplastic large cell lymphomas, primary cutaneous CD30-positive T-cell lymphoproliferative disorders and embryonal carcinomas. Occasionally, diffuse large B-cell lymphoma stains with this antibody. This antibody also stains plasma cells in paraffin-embedded tissue and reactive immunoblasts.