An asymmetrical opening RF surgical resection loop comprises a short electrically non-insulated loop section and a long electrically insulated loop section, where the distal ends of the loop sections are interconnected. Furthermore, a manipulation wire guided in an insulated catheter and displaceable in the longitudinal direction thereof is connected to this loop section in order to slide the long loop section out from the catheter. The short loop section is withdrawn from the catheter by the long loop section. An insulated stop wire is connected to the short loop section and is also pulled out a predefined length from the catheter by this, where at least the pulled out section of the stop wire is electrically insulated. By means of an entrainer device, the stop wire and the short loop section connected to this is withdrawn into the catheter upon withdrawal of the manipulation wire.
