Abstract: Disclosed is a medical vascular guide wire made of a synthetic resin hollow monofilament. The guide wire is comprised of a tip part, a flexible part having a smaller diameter than the other parts, a tapering part and a manipulating part, these four parts continuously forming in line, in that order, along the monofilament axis. At least the tip part and the manipulating part have X-ray impermeable material inserted in the respective hollows thereof. A self-guiding type catheter made of a synthetic resin, multi-hollow monofilament is also provided.