A method and apparatus (10) for determining accurately the location of the tip (14) of a catheter (16) inside biological tissue is disclosed including a locator (34) having a coil (38) wound axially on a core (36) and a detector (12) in the form of a coil (28) wound on a core (24) removably positionable within catheter (16) adjacent the tip (14). A controller (20) generates AC current to coil (38) to produce an electromagnetic field and compares it with the output voltage developed in coil ( b 28) when the locator (34) comes within close physical proximity to detecetor (12). Locator (34) includes an amber LED indicator (42) which is energized when the locator (34) is behind the detector (12) and the monitored output voltage is in phase with the generated alternating current and includes a red LED indicator (44) which is energized when the locator (34) is beyond the detector (12) and the monitored output voltage is 180.degree. out of phase with the generated alternating current. The controller (20) includes a beeper (48) which provides an audible indicator when energization changes between the indicators (42, 44).