AbstractThe reaction products of five peptides with diethylpyrocarbonate, a site‐specific reagent for histidine residues and amino groups, have been synthesized, isolated by high‐performance liquid chromatography (HPLC) and identified by fast‐atom bombardment (FAB) mass spectrometry. Peptides containing histidine, as well as compounds resulting from the N‐carboethoxylation of terminal amino groups and the histidine imidazole ring, provide a derivative produced by cleavage of the histidine heterocyclic ring through a Bamberger reaction. The main masss spectral features of these derivatives are discussed in comparison with structurally related compounds. HPLC along with with FAB MASS spectrometry shows itself to be a suitable technique for the characterization of these structures.