An instrument for ultrasonics lithotripsy comprises a probe which is applied to the stone which is to be disintegrated, which may be placed in oscillation by means of a piezo-electric sound transducer which is assembled from ceramic discs. The transducer is energized into oscillation by an electrical generator and the transducer oscillations are transmitted to the probe via a distal transducer closure. A particularly effective operation of the instrument is the result if the transducer is energized only intermittently by pulsed operation of the generator, no specific natural resonance frequencies of the system being intended to occur within the preset range of operating frequency.