Abstract: Device consisting of an auxiliary catheter (9), a fastening element (13), and a blocking device (11), designed in such a way that a partial catheter (2) can be mounted and secured at the end of the auxiliary catheter until the partial catheter has been placed in the desired position in a body cavity, especially the urethra, after which the partial catheter can be detached from the auxiliary catheter by manipulation of the blocking device and the fastening element, so that only the partial catheter is left in the desired position in the body cavity.