A device for introducing a catheter guide wire into a vessel of a patient has a connector and a straightener for a J-shaped end of the guide wire, the connector having an axial bore, and its distal end and proximal end permitting a connection of the Luer type to a needle and to a syringe, respectively. The connector supports, on its inside, a sealing valve equipped with a slit, and the axial bore has, in its portion between the sealing valve and the distal end of the connector, a leaktight mating surface, the shape of which is such that it permits liquid-tight mating with the outer surface of the distal end of the straightener, when the latter is introduced into the connector via the sealing valve.
