Peritoneal mast cell from a Beige rat undergoing anaphylactic degranulation of giant secretory granules. Swollen, less electron-dense secretory granules in the process of extrusion are enlarged beyond the giant, electron-dense cytoplasmic secretory granules not so involved. Original magnification × 12,000. (Courtesy of Ann M. Dvorak, MD, Department of Pathology, Beth Israel Hospital, Harvard Medical School, 330 Brookline Ave, Boston, MA 02215.)