The influence of non-ionic surfactant molecules on polymer interdiffusion in poly(butyl methacrylate) (PBMA) latex films was investigated using the non-radiative energy transfer technique. It was found that nonylphenoxypoly(ethylene oxide) surfactants such as NP-20 and NP-100 act as plasticizers to enhance the polymer diffusion rate. The increase in diffusion rate with the increase in surfactant concentration is in complete accord with the Fujita-Doolittle free volume model. This suggests that by the time the latex dispersion is dry, the surfactant has diffused uniformly into the latex polymer.