The effect of five organic solvents on polymer diffusion across particle interfaces in poly(butyl methacrylate) latex films annealed above their glass-transition temperature has been studied by fluorescent nonradiative energy transfer. Diffusion coefficients and penetration depths of polymer chains were calculated by assuming a Fickian diffusion. Their variations upon annealing time were found to depend on the nature of the organic solvent. A qualitative model describing the variation of penetration depth with time, accounting for solvent plasticizing effect and evaporation, is presented.