The potential of space-borne synthetic aperture radar interferometry (InSAR) to estimate both magnitude and spatial pattern of slope motion in a periglacial environment has been evaluated over a large area of the western Swiss Alps, using data from the ERS-1 and ERS-2 satellites. About 280 active rock glaciers with different classes of velocities have been identified on the analysed interferograms. The velocities range from a few centimetres per year to several meters per year. This data was validated by some differential GPS measurements and compared to numerous field observations. The resulting classification permits a better description of the full range of rock glaciers velocities and dynamics. Therefore, ERS InSAR reveals to be an efficient remote sensing technique, not only for inventorying active rock glaciers over a wide area, but also to estimate and categorize their displacement velocities.