The application of radar interferometry to detect slope movements on the order of millimeters to centimeters per year is demonstrated. The deformation field of a slope above a hydropower reservoir in the Austrian Alps was derived from SAR interferometric pairs of the satellites ERS-1 and ERS-2, acquired between July 1992 and August 1998. Above the treeline it was possible to map the motion from interferograms covering time spans up to three years. Whereas ground-based geodetic measurements focussed on the movements of the lower slope section, the interferometric analysis shows that the mass wasting processes affect the entire slope of 1000 m vertical extent. Significant interannual differences of the displacement rates became apparent which were found to be related to the pattern of summer rainfall. ¿ 1999 American Geophysical Union