The present invention concerns an assembly for inserting a catheter (22) into a body lumen, the assembly (10) comprising a introduction device (11) to be introduced into an aperture of the body lumen, an elongate fixing element (16) having a proximal and a distal end, wherein with its distal end the fixing element (16) is securable to the introduction device (11), and wherein at the proximal end of the fixing element (16) a clamping device (14) is provided, which clamping device (14) comprises a clamping unit (17), for securing a guide wire (27) in relation to the introduction device (11), and which clamping unit (17) comprises a passageway for the guide wire (27). Further, the assembly (10) comprises a catheter (22), having a proximal end and a distal end, wherein the proximal end comprises means (29) for releasably engaging the clamping unit (17), and wherein by engagement of the means (29) of the catheter (22) with the clamping unit (17) the guide wire (27) is movable through the introduction device (11) and wherein, upon disengagement of the means (29) of the catheter (22) from the clamping unit (17), the guide wire (27) is non-movably secured relative to the introduction device (11).
