Implanted arterial catheters permit recording, sampling, and injecting when used in unanesthetized and undisturbed dogs or cats. The catheters are made of silicone rubber tubing fitted to plastic Luer hubs which terminate in resealing rubber serum caps. The catheters are inserted into the descending aorta via the carotid artery and are brought out through the skin on the back of the neck. Results indicate that they can be expected to function for several weeks. Note: (With the Technical Assistance of Robert L. Dauber and F. Richard Darrow) catheters, chronic; catheters, implanted; silicone rubber tubing Submitted on July 13, 1964