Since 20 years surveys have been undertaken to find OH/IR stars in the central parts of our Galaxy using various radio telescopes around the world. The present paper gives a review of such surveys and of dynamical studies using their data. Presently, two major survey projects are going on: a deep search in the very Centre of the Galaxy using both VLA monitoring data and new AT data and a large-scale survey of the area |l| <= 45\deg, |b| <= 3\deg also using both VLA and AT data. The fact that only three parameters per OH/IR star are known - the two sky coordinates and the line-of-sight velocity - implies that severely limiting and simplifying assumptions have to be made regarding the distribution function of the stars and the gravitational potential. Usually spherical symmetry and isotropic velocity dispersion have been assumed. Recently, a project has been initiated to determine the proper motions of the OH/IR stars close to the Galactic Centre using the VLA and the VLBA on the associated H_2O and SiO masers. It is pointed out that the analysis of l-v diagrams so far has overlooked the fact that they are superpositions of many l-v diagrams from concentric ring areas within the total area. The slopes of the regression lines of these 'inner' l-v diagrams get increasingly larger for smaller areas. The 'l-v slope' as a function of galactocentric distance is that expected for differential rotation in an r^-2 mass density distribution, a fact which also is suggested by the surface density distribution of the stars.