A guide wire for a catheter is disclosed that includes a core wire and a sheath for covering at least the distal end of the core wire. The core wire is formed from a nickel-titanium alloy having a nickel-titanium ratio in the range of 3:2 to 1:1. The core wire is worked in a manner such that in a tensile test wherein the core wire is elongated by at least 5%, the core wire has a recovery percentage of at least 90%. Additionally, elongations in the range of zero and 5% do not cause any stress-induced martensitic transformations and/or austinite reverse transformations. Thus, the load-elongation characteristics of the nickel-titanium alloy are such that the load increasing rate is either proportional or gradually decreasing throughout the elongation range of 0 to 5%.