The smallest supermassive black hole with a well-determined mass has M bh ≈ 10 M ☉. The existence of black holes in the mass range 10 –10 M ☉ (" intermediate-mass black holes ") is predicted by the M – σ relation in low-mass galaxies, and the existence of intermediate-mass black holes has been reasonably well established in a number of galaxies that contain active galactic nuclei, although the values of M bh in these galaxies are very uncertain. No clear evidence has been found for ultra-massive black holes with masses above 10 M ☉, although this may be an expected consequence of the observed upper limit to σ.