Pentosidine, a crosslink amino acid in which one arginine and one lysine residue are linked together by a pentose, has been detected in foods for the first time using ion-exchange chromatography with direct fluorescence detection and subsequent ninhydrin derivatization. The method allows the simultaneous quantification of pentosidine along with all other amino acids of acid hydrolyzates at levels lower than 50 mu g kg protein. Levels of pentosidine in all food samples investigated were very low (milk products between not detectable and 2-5 mg/kg protein; roasted coffee and some bakery products up to 35 mg/kg protein), indicating that pentosidine does not play a major part in the polymerization of food proteins.