The cellular origin and the type of proliferation of the Hodgkin and Reed-Sternberg (HRS) cells, the malignant cells of Hodgkin's disease (HD), is an issue of constant debate. Immunohistochemical and molecularbiological studies of different research groups revealed contradictory results among the different groups ranging from a complete absence to a frequent presence of B-cell or T-cell characteristic features in the HRS cells. The determination of their clonality by cytogenetic means produced no conclusive results. To unequivocally clarify these questions we and others isolated single HRS cells and amplified their immunoglobulin (Ig) rearrangements. Most groups found Ig rearrangements within the HRS cells pointing to a B-cell nature of these HD cases. Individual IgH rearrangements were found in a proportion of the HD cases whereas most cases harbor monoclonal HRS cells with or without additional polyclonal rearranged HRS cells. Further studies are needed to clarify whether the differences among the different groups are caused by the selection of the HD cases used for investigation.