Film formation by a surfactant-stabilized, peroxide-initiated styrene/butyl acrylate latex was followed in situ by ultramicroscopy. The effects of latex serum components on film formation were observed first by the subjection of the latex to extensive dialysis and then by the separate addition of salt and surfactants. Domains of different particle concentrations were observed in the latex dispersion during liquid evaporation, and their positions were related to those of defects in the dry film. Films obtained with the dialyzed latex showed macroscopic defects, which were not seen in the as-prepared latex. Partially reconstituted latex (dialyzed, with the later addition of salt but not surfactant) behaved like the as-prepared latex. (C) 2002 Wiley Periodicals, Inc.872159167