A needle guide to reach inaccessible vessels in an intact animal may be made from polyethylene tubing (4 to 6 mm. outside diam.) by blowing a curved end plate or foot which is perforated circumferentially so that it may be sutured to a vessel. The lumen of the tube is sealed by a thin plastic membrane at the end plate in order to (1) indicate the immediate proximity of the vessel beneath when the resistance of the membrane is felt with the needle, (2) support the tip of the needle, (3) control by tamp-onade any hemmorrhage when the needle is withdrawn. The outer end of the guide is sutured in subcutaneous tissue. A smaller polyethylene tube with a cup-shaped external end may be inserted. These needle guides have been employed to obtain blood and the measure pressures in the pulmonary artery and left auricle in intact unanesthetized dogs.