The origin and role of confronting cisternae (CC) have been clouded in mystery since their discovery in 1955. Early investigations suggested that CC arose from either nuclear envelope (NE) or by stacking of endoplasmic reticulum (ER) cisternae. Electron microscopic studies of mitotic HeLa cells suggest that CC are fragments of NE (Fig. 1) that arise as portions of the NE fold back on one another. Because lamin B is a NE specific protein, a monoclonal antibody to lamin B was used to probe the origin of CC. The monoclonal antibody to lamin B was then detected by utilizing a secondary antibody conjugated to the fluorochrome rhodamine which fluoresces red when exposed to UV light. Fluorescent microscopy of interphase HeLa cells demonstrates that only the NE fluoresces red when the cells are probed with a monoclonal antibody to lamin B (Fig. 2). There is no label localized in the cytoplasm which supports the evidence that lamin B is only localized to the NE in interphase cells.