A medical probe such as a catheter (
) is guided within the body of a patient by determining the relative positions of the probe relative to another probe, as by transmitting non-ionizing radiation to or from field transducers (
) mounted on both probes. In one embodiment, a site probe (
) is secured to a lesion within the body, and an instrument probe (
) for treating the lesion may be guided to the lesion by monitoring relative positions of the probes. Two or more probes may be coordinated with one another to perform a medical procedure.