A simple, sensitive fluorescence method for following quantitatively the rates of diffusion of guest molecules in native polymer films is demonstrated using three N,N-dialkylanilines (DAA; alkyl = methyl, ethyl, and n-butyl) as guests and low density polyethylene (LDPE) as the polymer. Both Fickian and first-order rate models are used. The results are compared with those obtained previously using LDPE films with fluorophores attached covalently to interior chains. They indicate that diffusion occurs as a distribution of event types whose ensemble average is being measured. The very high and similar diffusional activation energies calculated for the three DAA in LDPE are consistent with a microscopic model in which polymethylene chain motions in addition to those experienced normally by the polymer are required to move the guest molecules. It is suggested that synchronous motions of at least two vicinal chains may be necessary.