Following enzymic hydrolysis, sensitive and unambiguous determination of the protein-bound Maillard compound pyrraline, a lysine derivative with a pyrrol structure, was achieved by ion-exchange chromatography with photodiode array measurement and subsequent ninhydrin detection. The method allows the simultaneous quantification of pyrraline in addition to the common amino acids, as well as acid-labile components such as the Amadori products and tryptophan, at levels lower than 500 mug/kg protein. Values of pyrraline in controlled heated samples first increased linearly with heating time, followed by a significant decomposition after long-term heating. In severely heat-treated samples (110-degrees-C for 5 h), up to 5.6% of the initial lysine residues had reacted to the pyrrolaldehyde.