The invention relates to a catheter for the withdrawal of blood, comprising a catheter tube (1) and a return line (3) located therein. The catheter tube (1) and the return line (3) located therein each have a length such that it is possible to advance the catheter tube (1) into a large-volume vein. One end of a terminal region (31) of the return line (3) facing away from the end (11) of the catheter tube (1) is fastened on the inner wall of the catheter tube (1) at a site (4) in such a way that the terminal region (31) in the catheter tube (1) floats such that the opening of the terminal region (31) is firmly located in the longitudinal direction in the region behind the opening of the end (11) of the catheter tube (1). <IMAGE>
