Monodisperse copolymer particles from 1.1 to 2.6 mu m in diameter were obtained by unseeded batch dispersion copolymerization of styrene and butyl acrylate in an ethanol-water medium. A two-level factorial design using bottle polymerizations was initially carried out including the following variables : stabilizer concentration, initiator concentration, polarity of the dispersion medium, initial monomer concentration, and temperature. Once the region of experimental conditions in which monodisperse latexes can be prepared was identified, further effort was devoted to analyze the effect of other variables. It was found that the temperature at which nucleation occurs and the evolution of the temperature after the onset of nucleation were critical to obtain monodisperse particles. The particle size increased with increasing initial monomer concentration and ethanol-water weight ratio, and decreasing stabilizer concentration. A minimum quantity of emulsifier was necessary to avoid coalescence of particles and to obtain monodisperse particles.