Instruments and methods for tracking such instruments in a human patient. One embodiment of an instrument in accordance with the invention comprises an elongated body, such as an elongated flexible member, which has a distal section configured to be passed through a vessel or other passageway in a human. The instrument can further include a lumen through the distal section and a magnetic marker having a transponder at the distal section. The transponder includes a circuit configured to be energized by a wirelessly transmitted magnetic excitation energy and to wirelessly transmit a magnetic location signal in response to the excitation energy. The magnetic marker, for example, can be attached to or otherwise integral with the instrument.
