The diffusion of N,N-dimethylaniline and N,N-dioctadecylaniline from a low-density polyethylene film into 2 N hydrochloric acid was measured in real-time at various temperatures by fluorescence spectroscopy. Diffusion coefficients (D) were obtained from each data set by a best fit to a series expansion of the integrated form of Fick’s second law for diffusion through a film. The activation energies for diffusion (E-D) were calculated from the D values in a temperature range above the glass transition and below the melting transition assuming Arrhenius behavior. As expected, N,N-dioctadecylaniline diffusion was slower than that of N,N-dimethylaniline at one temperature. Somewhat surprisingly, good fits of the N,N-dioctadecylaniline data sets to the series expansion require a model with two concurrent, independent diffusion processes; two diffusion coefficients at each temperature and two values of E-D, 16 +/- 4 and 4 +/- 1 kcal/mol, are calculated. The significantly higher activation energy, similar in magnitude to the single ED of N,N-dimethylaniline, 15.7 +/- 0.4 kcal/mol, is associated with the more rapid diffusional component. The data are discussed in terms of the type of sites occupied by the anilines and the influence of the two molecules on their local environments.