Abstract: The invention relates to a combined ultrasound and HF surgical system, including at least one ultrasound generator which operatively provides an excitation signal through which an ultrasound converter can generate an ultrasound vibration, at least one HF generator which operatively generates HF energy, and at least one ultrasound and HF instrument electrically connected with the HF generator and the ultrasound generator, wherein the ultrasound vibrations and the HF energy are introducible into biological tissue through the HF instrument which includes at least one ultrasound converter and at least one HF electrode. In order to be able to use HF energy and ultrasound energy simultaneously without damaging the instrument or wearing the it out, the system includes a protective device which prevents sparks operatively generated through HF energy or reduces the probability of occurrence of the sparks.