A method of operating an apparatus for the sterilization of plastics material containers is provided, wherein charge carriers are generated in a working operation and are conveyed through a guide chamber and emerge from this guide chamber by way of an outlet window bounding this guide chamber and wherein the outlet window is introduced into the plastics material containers at least in part through an aperture of the aforesaid plastics material containers during the sterilization of the plastics material containers. The outlet window is acted upon with a flowable cleaning medium in a cleaning operation of the apparatus.