A miniature catheter suitable for clinical use based on the principle of the continuously everting tube has been developed and tested extensively in dogs. The 1-mm-dia flexible tube can advance up a narrow tortuous blood vessel 30 cm beyond the tip of the conventional catheter to which it is attached. A slippery hydromer coating combined with a U-shaped cross section enables the tube eversion to be accomplished at an acceptable operating pressure. The new system will provide access to previously inaccessible regions of the body, and has the potential for clinical use in embolizing selected vessels, providing highly localized chemotherapy, and sampling body fluids. The catheter can advance both with and against the blood flow in arteries and veins, and is awaiting clinical trials.