OH/IR stars are ideal probes of the gravitational potential in the central parts of our Galaxy. It is believed that most stars go through this short phase in their evolution, and as stars, their motions are governed only by gravity. The characteristic signature of their OH masers make them easily identifiable and enables their radial velocities to be measured directly. Their OH luminosities are sufficiently high for them to be detected throughout the Galaxy.

Since more than 20 years surveys have been carried out to find OH/IR stars in the central regions of the Milky Way using various radio telescopes around the world. I will present these surveys in my talk.

I will then give a short summary of stellar dynamics from an experimentalist's viewpoint. The main part of my talk will be focussed on a new way of looking at the data and its implications. The principle tool in the dynamical analysis of OH/IR stars so far has been the so-called l - v diagram, radial velocity as a function of Galactic longitude. I will demonstrate that l - v diagrams for longitudes out to +/- 15 deg are the superposition of an ensemble of l - v diagrams with regression slopes which are decreasing with increasing area of sky around the Galactic center. My conclusion is that the Galactic bulge is rotating differentially. This is in contrast to all other studies of the bulge which have mostly pointed to solid-body rotation.