Skin biopsy specimens from normal skin and from 115 patients with benign dermatoses, pre- or pseudo-malignant disorders or malignant cutaneous lymphomas have been examined immunohistologically for expression of the Reed-Sternberg cell associated antigen CD30 detected by monoclonal antibodies Ki-1 and Ber-H2. The antibodies stained the atypical cells in lymphomatoid papulosis, a proportion of the neoplastic cells in some cases of mycosis fungoides and most of the neoplastic cells in six large cell anaplastic/pleomorphic non-Hodgkin's lymphomas. The lymphoid cells in all other specimens were Ki-1- and Ber-H2-negative. In all cases, expression of the Ki-1/Ber-H2 antigen was accompanied by expression of activation and proliferation associated markers (i.e., HLA-DR, IL-2 receptor, transferrin receptor and the Ki-67 nuclear antigen). These data indicate the value of antibodies Ki-1 and Ber-H2 in distinguishing between lymphomatoid papulosis and other types of pre- or pseudo-malignant disorders and support the view that lymphomatoid papulosis, Hodgkin's disease and some types of non-Hodgkin's lymphoma constitute a spectrum of related disorders, originated from activated lymphoid cells.