  The azimuthal version of the magnetorotational instability (MRI) is a
non-axisymmetric instability of a hydrodynamically stable differentially
rotating flow under the influence of a purely or predominantly azimuthal
magnetic field. It may be of considerable importance for destabilizing
accretion disks, and plays a central role in the concept of the MRI dynamo. We
report the results of a liquid metal Taylor-Couette experiment that shows the
occurrence of an azimuthal MRI in the expected range of Hartmann numbers.
