Abstract: The invention relates to a labelled peptide compound, wherein the peptide has a selective neurotensin receptor affinity and is represented by the general formula R1—(1Pro)n—2Xaa—3Xbb—4Xcc—5Xdd—6Xee—7Leu—OH(SEQ ID NO.2)  (I) wherein: R1 is a (C1-C3)alkanoyl group, an arylcarbonyl group, an aryl-(C1-C3)alkanoyl group, or a chelating group attached by an amide bond or through a spacing group to the peptide molecule; Xaa and Xbb are each individually Arg or Lys; Xcc is an unsubstituted or substituted cyclic amino acid, preferably selected from Pro and Hyp; Xdd is Tyr, Trp or Phe; Xee is Leu, Ile or t.

Abstract: The invention relates to a labelled peptide compound, wherein the peptide has a selective neurotensin receptor affinity and is represented by the general formulaR.sub.1 -(.sup.1 Pro).sub.n -.sup.2 Xaa-.sup.3 Xbb-.sup.4 Xcc-.sup.5 Xdd-.sup.6 Xee-.sup.7 Leu-OH (SEQ ID NO:2) (I)wherein:R.sub.1 is a (C.sub.1 -C.sub.3)alkanoyl group, an arylcarbonyl group, an aryl-(C.sub.1 -C.sub.3)alkanoyl group, or a chelating group attached by an amide bond or through a spacing group to the peptide molecule;Xaa and Xbb are each individually Arg or Lys;Xcc is an unsubstituted or substituted cyclic amino acid, preferably selected from Pro and Hyp;Xdd is Tyr, Trp or Phe;Xee is Leu, Ile or t.-butylalanine; andn is 0 or 1;and wherein said peptide is labelled with (a) a metal isotope, or (b) with a radioactive halogen isotope; on the understanding that:(i) if the label is a metal isotope, R.sub.