Abstract: An intravenous catheter assembly comprises a catheter having an elongate hollow tube and a hub connected to said tube. The hub has an interior cavity communicating with the lumen of the tube and also includes an aperture communicating with the cavity. A needle is slidably positioned in the aperture and the lumen of the tube so that its pointed end protrudes slightly beyond the distal end of the catheter tube. An operable valve includes a closure portion located in the cavity and is adapted to close the interior entrance of the aperture under the influence of fluid flowing into the cavity from the lumen after the needle is withdrawn. The operable valve also includes an activating portion located outside the exterior entrance of the aperture and is adapted to be moved generally axially to thereby move the closure portion away from the aperture and open the same for fluid flow into the cavity.