MM 4-64 (FM 4-64) is the abbreviation of our Membrane Marker 4-64, chemically called N-(3-triethylammoniumpropyl)-4-(6-(4-(diethylamino)phenyl)hexatrienyl)pyridinium dibromide. In literature this membrane marker is also called "FM 4-64" (FM® is the trademark of Molecular Probes). It is a lipophilic styryl dye that is used as a vital stain to follow bulk membrane-internalization and transport to the vacuole in yeast. MM 4-64 is a sensitive reporter of vacuolar dynamics, detecting such events as segregation structure formation during mitosis, vacuole fission/fusion events, and vacuolar morphology in different classes of vacuolar protein sorting mutants. It can be used for detecting endosome to vacuole membrane transport in vitro.