High-frequency chirurgiegeraet for the thermal coagulation of biological tissue.

The HF surgical tool has an HF generator (1) coupled to the coagulation electrodes (13) via a manual or automatic switch (21,22) with automatic cut-out of the current at the end of the coagulation process. A current monitor (25) is used to monitor the amplitude variations of the HF current (IHF) or the corresponding voltage (HHF) during the coagulation interval, its signal being converted into a DC voltage (Ua) representing the amplitude variations and a second DC voltage (Ub) representing the peak amplitude. The first voltage (Ua) is compared with a given fraction of the second voltage (Ub) to control a bistable stage used for initiating the automatic current cut-out.