Light emitting compounds of the formula: ##STR1##

where R₁ is a light-emitting moiety, R₂ is a bombesin-like peptide and fragment, derivative or analog thereof and L is a linker moiety, which may be present or absent. The peptide is linked at a first amino acid position to (C—X) which, in turn, is selected from the group including CO, CS, CH(OH), CC=O, CNH, CH₂, CH(OR), CH(NR), CH(R), CR₃R₄, and C(OR₃)OR₄ where R, R₃, and R₄ are alkyl moieties or substituted alkyl moieties. Optionally the compound may include a linker moiety between the peptide and the C—X binding group. Preferably, the compound exhibits substantial biological activity in the presence of receptors having affinities for bombesin-like peptides.