Small amounts of organic solvents are often postadded to latex dispersions as aids to promote film formation. However because of their toxicity, the use of these solvents will be prohibited in the near future. An alternative solution to this problem may be the use of new tailored core-shell particles. We have monitored the extent of mixing of the latex particles during film formation using the fluorescent nonradiative energy transfer technique. We report promising results obtained with poly(butyl methacrylate) core-copolymer (butyl methacrylate-butyl acrylate) shell latex particles. We show that films obtained from these dispersions are comparable to those obtained from solvent-added poly(butyl methacrylate) latex dispersions in terms of polymer interdiffusion across particle boundaries.