Serous effusions of nine of 33 patients with systemic lupus erythematosus contained lupus erythematosus (LE) cells, identifiable in Papanicolaou‐stained smears, wet films stained with toluidine blue, and cell blocks stained with haematoxylin and eosin. Specimens in which LE cells were found contained at least a moderate number of polymorphonuclear neutrophilic leucocytes. Most specimens containing LE cells also contained cells that resembled LE cells (tart cells), which appeared to be small macrophages that had phagocytosed a non‐homogenized nucleus of a cell that had undergone degeneration. In 34 years of cytologic practice we have recognized LE cells in serous effusions only from patients who were already diagnosed as having systemic lupus erythemato