The immunophenotype of the Reed-Sternberg cells in Hodgkin's disease is heterogeneous among different cases; this heterogeneity has contributed to the continuing uncertainty regarding the normal counterpart of the Reed-Sternberg cell. In this study, the authors demonstrate coexpression of the B-cell marker, CD20, and the granulocyte associated antigen, CD15, by Reed-Sternberg cells in three of 20 cases of nodular sclerosis and mixed cellularity Hodgkin's disease using a double-labelling technique in one case and staining of serial sections in three cases. Additionally, the authors found that expression of CD20 occurred more often in tumors with a monomorphous proliferation of mononuclear and binucleate Hodgkin's and Reed-Sternberg cells, without numerous eosinophils or polymorphonuclear neutrophils. In contrast, expression of CD15 by Reed-Sternberg cells was associated with a greater granulocyte infiltrate. The presence or absence of fibrosis, plasma cells, and histiocytes did not correlate with antigen expression. These results suggest that there may be a continuum of antigen expression by Reed-Sternberg cells, with some cells expressing CD20, some CD15, and others expressing both antigens; cells coexpressing both CD15 and CD20 may represent an unstable intermediate in the process of antigen switching. The possibility that antigen expression by the neoplastic cells in a given case may modulate depending on the background infiltrate could explain the heterogeneity of immunophenotype among cases of Hodgkin's disease.