Abstract: Specific metal-chelating precursors incorporating a pendant protected (e.g. with Fmoc) amino acid functionality are synthesised. The pendant amino acid functionality allows the chelator to be inserted into a synthetic peptide sequence during standard solid-phase peptide synthesis at any predetermined position in the sequence, in place of lysine or any other amino acid, or in addition to native amino acids. An example is a conjugate incorporating Fmoc-protected L-lysine and the technetium-binding group hynic (hydrazinonicotinamide), shown as molecule 1 in FIG. 1 of the accompanying drawing. These molecules permit synthetic approaches with greater flexibility and control of the site of labelling than conventional methods.