Abstract: A connector which is adapted to be connected to a plastic cannula or a vein catheter comprises a tubular and/or conical portion that is adapted to be tightly joined to a parenteral solution supply needle and/or to a hose provided with a cone fitting. To ensure that a metal cannula or a vessel catheter can be pushed through the connector without obstruction and that the connector closes automatically as soon as the metal cannula or the catheter or the cone fitting of a supply hose has been pulled from the connector, the body of the latter is provided with a receptable, which is radial with respect to the flow passage, and a disc consisting of elastomeric material and having a central slit is held in said receptacle and blocks the flow passage.