A guide wire with a distal portion having adjustable flexibility. The guide wire may include a distal polymeric member and a heat source. The heat source may be activated to cause the polymeric member to increase in temperature and increase in flexibility. The increase in flexibility of the distal portion of the guide wire enhances the ability of the guide wire to navigate tortuous vasculature to a target site. After the guide wire has been navigated to the target site, the heat source may be deactivated to cause the polymeric member to decrease in temperature and increase in stiffness. The increase in stiffness of the distal portion of the guide wire enhances support provided for devices (e.g., catheters) advanced thereon.