The diffusion of the ultraviolet stabilizer 2,4dihydroxybenzophenone in compressionmolded sheets of low-density polyethylene, high-density polyethylene, and isotactic polypropylene was investigated over the temperature range of 44-75Β°C. The magnitude of the diffusion coefficients for these polyolefins was found to decrease in the order lowdensity polyethylene > high-density polyethylene > polypropylene, the corresponding activation energies being approximately 18, 23, and 34 kcal/mole. Studies under conditions of saturation indicated that the migration of this stabilizer was confined to the more accessible amorphous regions of the polymers. The rate of loss of stabilizer from polymer samples immersed in water was also investigated at 44Β°C. Values of the diffusion coefficients calculated from the results of these studies were somewhat greater than those determined from the diffusion studies for the low-density polyethylene and isotactic polypropylene samples and considerably smaller in the case of high-density polyethylene. The extraction studies also permitted the quantitative evaluation of the solubilities of the stabilizer in the polymers. These were found to be 0.003, 0.03, and 0.07 wt-% for high-density polyethylene, low-density polyethylene, and polypropylene, respectively, a t 44Β°C.