Abstract: An intravascular loop probe includes two lenticular, compressible, resilient, and expansible wire loops disposed in planes substantially mutually perpendicular to each other for operation in a conduit traversed by a magnetic field externally applied. The loops are insulatively joined at the point of maximum curvature. The wires at the open ends of the loops continue as a wire bundle beyond a ground electrode and are cemented together to form a stem for inserting the probe into the conduit via a catheter. Central portions of loop wires are bared to serve as electrodes. The loop terminal wires which form the stem of the probe are connected to external circuitry so that each of the two orthagonal loops is serviced by a separate circuit.