The digestibility of wool in papain-bisulfite urea is increased by prior treatment with cold concentrated sulfuric acid, nitrous acid, or iodine but is diminished by 1- fluoro-2,4-dinitrobenzene, formaldehyde, chromium compounds, epichlorhydrin, propylene oxide, methyl iodide at pH's above 6, thiocyanate with acetic anhydride at pH's below 6, and, if applied to the reduced fiber, by 1,3-dibromopropane, acrolein, and methyl iodide at pH's above 7. Treatment with acid solutions of various aliphatic alcohols to esterify the carboxyl groups in wool likewise reduces the digestibility, maximum protection being obtained with methanol. The rapid method of measuring enzyme resistance used in these studies may be generally suitable for detecting wool damage and for selecting chemical methods of modifying wool for assessment by moth-resistance and soil-burial methods.