Abstract: The guide catheter system for use in the treatment of coronary artery disease includes a first single-lumen catheter of a relatively large internal diameter to pass a second guide catheter therethrough. The first guide catheter comprises an elongated flexible tube having a stainless steel braid embedded in the wall thereof for imparting desired torqueability characteristics to it. The first guide catheter is intended to be inserted at an appropriate point in the vascular system and then advanced until its distal end reaches the coronary ostium. The second guide catheter is fabricated by extruding a plastic, such as polyurethane thermoplastic resin over a tubular Teflon.RTM. core and because it is to be used within the lumen of the first catheter, it need not include a braided structure within its walls to prevent it from kinking.