Abstract: A thin walled intracorporeal catheter such as a guiding catheter employed for intravascular procedures which generally has an elongated catheter shaft with a polymeric wall with a stranded reinforcing structure having at least one strand and preferably most, if not all of the strands, formed of a metallic matereial containing at least 50%, preferably at least 65% by weight of a refractory metal such as molybdenum, tungsten rhenium, tantalum and niobium. The refractory metal containing strands of the reinforcing structure, which may have a circular or rectangular transverse cross-sectional shape, provide high levels of radiopacity with a high level of mechanical properties.