Changes in furosine, undenatured whey protein content, and proteolysis during 90 days storage at 20, 30, and 40 degrees C of UHT-processed milk were studied. Furosine increased as the temperature and storage time increased. The peptide concentration increased during the storage period, being faster at 30 degrees C than at 20 or 40 degrees C. High-performance liquid chromatographic analysis of undenatured whey proteins showed considerable changes in the shape of the peaks during storage.