A guide wire is provided to guide a very small diameter catheter, such as a coronary dilatation catheter used in coronary angioplasty techniques. The guide wire itself is of very small diameter, (under 0.020") yet is steerable and may be visualized fluoroscopically. The major portion of the guide wire is a small diameter flexible rod. The distal region of the rod is tapered. The tapered portion is surrounded by a helically wound spring which is brazed at its proximal and distal ends, to the base and tip, respectively, of the tapered region of the rod. A shorter segment of the spring extends beyond the distal end of the rod and serves as a highly flexible bumper to assure that the distal tip of the guide wire will not cause traumatic injury to the blood vessel. The distal region of the guide can be bent manually by the surgeon to a curved shape which it will tend to assume when relaxed. The distal region is flexible and can bend from the set curve to follow the contour of the blood vessel. The distal end of the wire can be steered by manipulation and rotation of the proximal end of the guide. At least the spring portion of the guide wire is formed from a material having a high degree of radiopacity to facilitate its fluoroscopic observation. Also disclosed is a combination of such a spring guide with a coronary dilatation catheter.