Abstract: A device for sterile storage of a catheter (11) and sterile advancing thereof a given length directly in a blood vessel, the device comprising a connecting piece (13), which is connectable both to a cannula and to a transparent, flexible protective sheath (15), in particular a plastic bag, enclosing the catheter. In order to allow continuous reading of the fed out catheter length the protective sheath (15) is equipped with a length scale (17), which has its highest value nearest the connecting piece (13) and which is made so that the reading of the length scale against the remaining length of the catheter in the protective sheath corresponds to the fed out length of the catheter. Further means (23;31;32;33) are provided which allow withdrawal of the protective sheath from wrinkled position to stretched position without bringing the catheter (11) with it.