Book paper deterioration in regions of high humidity and temperature is not always so serious as commonly supposed. Dehydration or overdrying seems more influential to deterioration than hydrolysis of cellulose fibers in paper. However, acidity of paper undoubtedly accelerates the degradation of book papers. Deacidification by alkoxy-magnesium carbonates in solvents and diethyl zinc are both effective in controling the degradation rate of acidic papers in accelerated aging tests, though less effective after degradation has taken place. Diethyl zinc can permeate into paper stacks with appropriate moisture contents, though the amount of zinc retained in paper is dependent on paper properties, such as density. -- AATA