The effect of temperature, pH and added salts on the degradation of collagen by the cupric ion - 3 percent hydrogen peroxide system was studied. The solubilization of steerhide corium collagen by the cupric ion-hydrogen peroxide system occurred over the pH range investigated (pH 2.5 to pH 8), but occurred much more readily below pH 4.5. Collagen was dissolved more rapidly by the cupric ion-hydrogen peroxide system at 30°C. than at 23°C. Addition of some metal cations to the cupric ion-hydrogen peroxide system at low concentrations did not affect the solubilization of the collagen by the system, but transition metal cations either increased or inhibited the solution of collagen. The solubilization of collagen by the cupric ion-hydrogen peroxide increased with time, until almost complete solubilization had occurred. When the added cation was Fe* h+3*s or Cr⁺³, the solubilization reaction did not go to completion. High concentrations of sodium chloride, sodium bromide, or sodium oxalate completely prevented solution of collagen by the cupric ion-hydrogen peroxide system. A saturated solution of sodium fluoride to a great extent inhibited the solution, while M sodium sulfate did not inhibit the activity of the system. Addition of trace amounts of ethylenediamine to the cupric ion-hydrogen peroxide system in the presence of 2 M NaCl restored to some extent to the system the ability to solubilize collagen. The importance of these findings in the aging and deterioration of leather, and in the choice of types of metal fittings to be used with leather is discussed.