Abstract: The present invention relates to compound having the formula: ##STR1## or a pharmaceutically acceptable acid salt thereof, wherein R is a polypeptide moiety comprises an amino acid sequence:-Y-Arg-Pro-Z-Ile-Leu;wherein Y is Arg, andZ is Tyr or Trp;R.sub.1 is a fluorophore selected from the group consisting of fluorescein, rhodamine, Blue fluorescent and Texas red; andX is oxygen or sulfur. The present invention also relates to a method for the labeling of neurotensin receptors on cell surface and a method to isolate neurotensin-receptor expressing cells.