The effect of cross-linking on intercellular polymer diffusion in poly(butyl methacrylate-co-butyl acrylate-co-ethylene glycol dimethacrylate) latex films containing 0.1-4 mol % ethylene glycol dimethacrylate (EGDMA) as a cross-linking agent was monitored by fluorescent energy-transfer measurements and by atomic force microscopy. The presence of cross-links in the latex particles limits the extent of polymer interdiffusion. The extent of mixing caused by this polymer diffusion decreased with increasing levels of cross-linking. Even, however, in films containing 4 mol % EGDMA, significant polymer diffusion occurred. To explain polymer diffusion in latex films with 100% gel content, we imagine that the intercellular mixing is caused by diffusion of dangling polymer chains anchored in the cross-linked network. These cross-linked latex particles form tough elastomeric films (with T-g estimated to be 10 degrees C), characterized by high tensile strength and substantial elongation to break (>100% elongation). The films have poor resistance to organic solvents.