Summary: Vacuolation of the cells of many tissues has been produced by feeding guinea‐pigs on Swainsona galegifolia.Medullary neurones, hepatocytes, hepatic sinusoidal cells and pancreatic acinar cells from such animals have been examined with the electron microscope.In each case the vacuoles have been found to be single membrane‐bound and to have no clear‐cut morphological relationship with the normal organelles.Their possible relationship with lysosomes is discussed.