Films composed of a mixture of poly(methyl methacrylate) (PMMA, M(w) = 306 000) and polystyrene (PS, M(w) = 234 000) were prepared by solvent casting. In these films, the PMMA component, covalently labeled with a fluorescent dye, comprised 10 wt % of the mixture. These films were examined by laser confocal fluorescence microscopy (LCFM). At depth greater than 5-6 mum below the surface, the blend morphology was one of tiny PMMA spheres dispersed in a continuous PS matrix. These spheres were randomly distributed in space and were characterized by a broad size distribution. At the surface, the morphology was very different. The PMMA was present in the form of large spheres, 5-6 mum in diameter, characterized by not only a very narrow size distribution but a strong periodicity in their location. The broad distribution of small particles in bulk can be attributed to phase separation by a nucleation and growth mechanism coupled with the small surface energy between PS and PMMA. At the surface, two other and larger surface energies come into play, those of PS/air and PMMA/air. In addition, more rapid evaporation of solvent from the surface may lead to a spinodal decomposition mechanism for surface phase segregation.