Abstract: An intravenous catheter is provided with a cannula and a needle-guide for the cannula. A support carries the needle-guide, and has a first end from which the needle-guide extends. The support is carried in a sheath, having a diameter sufficient to permit sliding of the support and having a length sufficient to accept the full length of the needle-guide. A retractor continuously urges the support to a position in which the needle-guide is withdrawn into the sheath. The sheath has a first end which defines an opening through which the first end of the support extends, and the sheath is capable of reducing the size of the opening upon insertion of the first end of the sheath into the cannula to grip the support, and returns to its original size upon withdrawal of the first end from the cannula to release the support and permit the withdrawal of the needle-guide into the sheath under the action of the retractor.