The major degradative process in γ-irradiated cellulose acetate is chain scission. For the dry powder the Gs value (number of scissions per 100 eV of energy absorbed) was found to be 7.1. The water-swollen material was found to degrade at the higher rate of Gs = 9.45. Additions of ethanol and methanol to the water brought about reductions in Gs, whereas dissolved nitrous oxide produced an increase in Gs. The useful life of cellulose acetate reverse osmosis membranes exposed to γ radiation was estimated by observations of the water permeation rate during irradiation. Membrane breakdown occurred at 15 Mrad in pure water, but the dose to breakdown was extended to 83 Mrad in the presence of 4% methanol.