The CD30 ligand (CD30L) is a type II transmembrane glycoprotein of the tumor necrosis factor ligand superfamily. Recent cloning of CD30L has enabled studies to explore its function and tissue distribution. For instance, recombinant CD30L has been shown to co-stimulate T cells and to act as mitogen for Hodgkin's disease (HD)-derived cell lines. The counter-receptor for CD30L, ie, CD30, is a type I cytokine receptor that is highly expressed by activated T cells, Hodgkin and Reed-Sternberg (H-RS) cells, and anaplastic large cell lymphoma cells. In the present study, recombinant membrane-bound and soluble human CD30L were instrumental to raise a monoclonal antibody (M80) recognizing membrane-bound CD30L on transfected and native cells. With this reagent, a panel of cultured lymphoma-derived cell lines as well as primary normal, reactive, and HD-involved lymphoid tissues were examined for expression of CD30L by immunostaining and flow cytometry. In reactive lymphnodes and tonsils, CD30L was expressed by a small subset of lymphoid cells, histiocytes, and granulocytes. Higher levels of CD30L expression were noted in HD lesions among bystander cells; ie, T cells and granulocytes that surrounded H-RS cells. Native CD30L displayed at the cell surface was functionally active as shown by the ability of fixed granulocytes to interact with CD30+ cell lines. Moreover, CD30L was detectable, although to a lower staining intensity, in primary H-RS cells of all HD tissues investigated regardless of the histological subtype and the phenotype of H-RS cells (ie, CD30+/CD40+ versus CD30-/CD40+). Co-expression of CD30 and CD30L that was seen on H-RS cells of all, except the CD30- nodular lymphocyte predominant, subtypes of HD may point to the use of this pair of molecules in paracrine and/or autocrine mitogenic cell interactions. Monoclonal antibody M80 may thus represent a useful tool for studying CD30L expression on cultured cell lines and primary cells from normal, reactive, and malignant tissues.