The high-energy collision-induced dissociation (CID) spectra of synthesized Amadori compounds, related to the exogenous opioid peptide morphiceptin, have been investigated. The spectra of [M H] ions of protected, partially protected and unprotected Amadori compounds exhibit mainly A-and Y@-type sequence ions. The protected compounds show peaks corresponding to the elimination of a C 3 H 6 O molecule, characteristic of a protecting isopropylidene group at the saccharide moiety. The position of the isopropylidene group in the partially protected Amadori compound has been derived from the CID spectrum of its [M Na] ion. A two-bond cross-ring cleavage reaction generates an ion at m/z 656, corresponding to the loss of a 90 Da neutral (C 3 H 6 O 3 ), and must originate from the C2-C3 isopropylideneprotected Amadori compound. The most intense ions in the CID spectrum of the [M H] ion of the unprotected Amadori compound arise from losses of water molecules. Comparison of the CID spectra of the [M H] ions of Amadori compounds with that for the parent peptide morphiceptin revealed a preferential A 1 -ion formation for Amadori compounds.