A locating system for determining the location and orientation of an invasive medical instrument, for example a catheter (
) or endoscope, relative to a reference frame, comprising: a plurality of field generators (
18, 20, 22
) which generate known, distinguishable fields, preferably continuous AC magnetic fields, in response to drive signals; a plurality of sensors (
30, 32, 34
) situated in the invasive medical instrument (
) proximate the distal end thereof which generate sensor signals in response to said fields; and a signal processor (
) which has an input for a plurality of signals corresponding to said drive signals and said sensor signals and which produces the three location coordinates and three orientation coordinates of a point on the invasive medical instrument.