Evidence is presented that cupric ions in the presence of hydrogen peroxide cause degradation of steerhide corium collagen and calfskin gelatin at room temperature by cleavage of the peptide chain; the results may be interpreted as a free radical-catalyzed depolymerization. Inhibitors of the reaction were studied. Elastin appears to undergo a similar reaction. A simple model dipeptide, glycylglycine, was used to investigate the depolymerization reaction and other secondary reactions which occur. The analogy of the depolymerization reaction to the similar deterioration of cellulose under the same conditions, and the relation of this reaction to the deterioration of leather on aging are discussed. Possible methods of preventing leather deterioration which takes -- AATA