To elucidate the lineage of plasmacytoid T cells, their immunophenotype was studied in reactive lymph nodes with a broad panel of monoclonal antibodies. Plasmacytoid T cells expressed several myelomonocytic markers, and almost all markers highly selective for macrophages. They lacked granulocyte-associated and B or T lymphocyte-associated antigens. These results provide strong evidence that plasmacytoid T cells are of monocyte lineage.