The influence of calcium carbonate deacidification on the rates of deterioration of commercial rag and newsprint papers at 90°C and 100% R.H. has been examined. Evidence is presented to show that the decreased rate of deterioration resulting from deacidification cannot be accounted for in terms of a decrease in the acid-catalyzed hydrolysis process alone. Atmospheric oxidation, shown to play an important role in the deterioration of the paper samples, is also retarded by deacidification.