A guiding member for use as an independent guidewire or as an integral part of a low-profile steerable dilatation catheter. The guiding member has an elongated main hollow tubular member, a tubular extension preferably made of polyimide secured to the distal end of the tubular member, a core member which is secured by the proximal end thereof within the inner lumen of the main tubular member and which extends through and out the distal end of the tubular extension and a flexible body, such as a helical coil, disposed about and secured to the distal portion of the core member which extends out the distal end of the tubular extension. The transverse cross-sectional area of the core member disposed within the inner lumen of the main tubular member should be at least 10%, preferably at least 25% less than the transverse cross-sectional area of the inner lumen of the main tubular member. The distal tip of the main tubular member is at least 15 cm, preferably between 25 and 60 cm proximal to the distal end of the coil to ensure that the transition region where the core member and the tubular extension join the main tubular member remains within the guiding catheter during vascular procedures therewith. When employed as part of a steerable catheter, the inflatable balloon is secured by the proximal end thereof to the distal end of the tubular extension and by the distal end of the core member which extends therethrough.