Immunohistochemical evidence that the plasmacytoid T cell is closely related to the blood monocyte has been reported, and the term plasmacytoid monocyte has been proposed to describe this cell. The present study was undertaken to analyze the presence and distribution of plasmacytoid monocytes in human reactive lymph nodes showing epithelioid cell reactions. Numerous plasmacytoid monocytes (detected by a panel of monoclonal antibodies) were found in the majority of the lymph nodes studies, usually in close topographical association with epithelioid cells and multinucleated giant cells. The present findings suggest that plasmacytoid monocytes may give rise to epithelioid cells. This is further supported by the ultrastructural similarities between plasmacytoid monocytes and plasmacytoid epithelioid cells, a cell type that has been identified previously in granulomas and considered a direct precursor of the classical epithelioid cell.