Labelled peptide compounds

A labelled peptide compound, wherein the peptide selectively binds to neurotensin receptors and is represented by the general formula

• R.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 tert-butylalanine;
• and
• n is 0 or 1;
• and wherein said peptide is labelled with (a) a metal isotope selected from the group consisting of .sup.99m Tc, .sup.203 Pb, .sup.67 Ga, .sup.68 Ga, .sup.72 As, .sup.111 In, .sup.113m In, .sup.97 Ru, .sup.62 Cu, .sup.64 Cu, .sup.52 Fe, .sup.52m Mn, .sup.51 Cr, .sup.186 Re, .sup.188 Re, .sup.77 As, .sup.90 Y, .sup.67 Cu, .sup.169 Er, .sup.121 Sn, .sup.127 Te, .sup.142 Pr, .sup.143 Pr, .sup.198 Au, .sup.199 Au, .sup.161 Tb, .sup.109 Pd, .sup.165 Dy, .sup.149 Pm, .sup.151 Pm, .sup.153 Sm, .sup.157 Gd, .sup.159 Gd, .sup.166 Ho, .sup.172 Tm, .sup.169 Yb, .sup.175 Yb, .sup.177 Lu, .sup.105 Rh and .sup.111 Ag, or (b) with a radioactive halogen isotope;
• with the provise that:
• (i) if the label is a metal isotope, R.sub.1 represents a chelating group for chelating said isotope;
• and
• (ii) if the label is a radioactive halogen isotope, said halogen isotope is attached to .sup.4 Tyr in the 2-position of the phenyl ring, to .sup.4 Trp, or to the aryl group of substituent R.sub.1.