Pathophysiological changes in ureteral kinetics can be monitored externally and non-invasively by means of a time-space matrix approach during the excretory phase of fast-frame routine renography. The main limitations of this method are poor space-time resolution and, in some cases, an inadequate visualization of the peristaltic waves. A new approach to the study of ureteral contractions using the power spectrum obtained from Fourier transforms of the ureteral time-activity curves was developed. The FORTRAN program was tested by an experimental simulation, and its subsequent application on fifty-one subjects indicated that the method is a useful complement to the space-time matrix technique. Moreover, evaluation of the power spectrum offers several advantages for the study of the pathophysiological parameters of peristalsis.