Samples of normal human dermis of different ages are reduced with tritiated sodium borohydride and changes of major reducible cross-links are compared as a function of chronological age. While lysinonorleucine practically remains constant, reduced desmosine changes slightly, hydroxylysinonorleucine and dihydroxylysinonorleucine display a marked decrease with age. An unknown compound is shown to increase with aging. The data suggest a correlation between the change of aldimine cross-links and the structural and/or biochemical changes occurring with increase in age.