Abstract: Primarily described are gel-forming systems, consisting of or comprising a composition (A), comprising one or several cationically crosslinkable polymer(s), and a composition (B), comprising one or several crosslinking agent(s) for crosslinking the cationically crosslinkable polymer(s) for use in a method for removing urinary calculi and/or fragments thereof, more particularly kidney stones and/or fragments thereof, from a region of the urinary tract, more particularly a kidney, that contains urinary calculi and/or fragments thereof, more particularly kidney stones and/or fragments thereof, that are to be removed, with the following steps: (i) providing the compositions (A) and (B), (ii) introducing the compositions (A) and (B) into a region of the urinary tract, more particularly the kidney, that contains urinary calculi and/or fragments thereof, more particularly kidney stones and/or fragments thereof, that are to be removed, under conditions enabling crosslinking of the cationically crosslinkable polymer(s