Hypervelocity stars move with extremely large Galactocentric velocities (~1000 km/s) and are found from their anomalous velocities, ages, and metallicities. These stars are thought to have interacted with the supermassive black hole at the center of the Milky Way, given that they are seen moving at large radial velocities relative to the Galactic center. Presumably, the SMBH's in M31 and the LMC (if it exists) should also produce hypervelocity stars, some of which may be moving at large velocities through the Milky Way but not necessarily along the line-of-sight relative to the Galactic center. Step one is to find the stars, next is to measure the mass of the SMBHs in M31 and the LMC by the rate of extragalactic hypervelocity stars.