Abstract: The method for identifying a sentinel lymph node located within a grouping of regional nodes at a lymph draininage basin associated with neoplastic tissue wherein a radiopharmaceutical is injected at the situs of the neoplastic tissue. This radiopharmaceutical migrates along a lymph duct toward the drainage basin containing the sentinel node. A hand-held probe with a forwardly disposed radiation detector crystal is maneuvered along the duct while the clinician observes a graphical readout of count rate amplitudes to determine when the probe is aligned with the duct. The region containing the sentinel node is identified when the count rate at the probe substantially increases. Following incision, the probe is maneuvered utilizing a sound output in connection with actuation of the probe to establish increasing count rate thresholds followed by incremental movements until the threshold is not reached and no sound cue is given the surgeon.