This is a report of data, which shows that linear polymers of the methacrylate class, in which the alkyl radical in the alcoholic group of the methacrylic ester contains hydrogen atoms located on tri-substituted carbon atoms, were sensitive to cross-linking under the influence of ultra-violet radiation at 60 degrees c. in a carbon-arc accelerated-fading apparatus. A filter of ordinary window glass was shown to reduce the rate of cross-linking of several polymers by a factor of 1.9. Certain ultraviolet-light absorbers based on substituted benzophenones were able to reduce the tendency of several polymers to lose their solubility. An attempt was made to estimate, on the basis of tests in the fadeometer and outdoors, the rate at which cross-linking might take place indoors. A chromatographic-leaching technique on paper was developed to measure the extent of cross-linking and the technique applied to polymers from test panels that were four to ten years old. These considerations led to the estimation that resistance to solution in a room well-illuminated by natural light should not be developed in polymers based on isobutyl and isoamyl methacrylate for perhaps 25 years. Because of the interest in the possible application of linear polymers to various problems in conservation, this detailed investigation was undertaken and is continuing.