Ultrafine black particles, ranging in diameter from 1 to 3 Am, were prepared by dispersion polymerization in a methanol/water mixture with vinyl monomers, nonpolymerizable Sudan black B dyes, and fluorescein isothiocyanate labeled charge control additives. Both the ratio of the methanol to the water dispersion medium and the polymeric stabilizer concentration had significant effects on the particle size. The important role of the stabilizer concentration lay in the particle formation step, during which it determined the particle stability and final particle size. These could affect the extent of the aggregation of nuclei by changing the adsorption rate of the stabilizer and the viscosity of the dispersion medium, resulting in smaller particles. The fluorescent-labeled charge control additives strongly affected the electrophoretic mobility. A small concentration of fluorescent-labeled charge control additives increased the electrophoretic mobility. However, a further addition reduced the electrophoretic mobility of the polymer particles. The concentration dependence of the fluorescent-labeled charge control additives on the deposition behavior in the polymer particles was successfully imaged and thereafter quantified by image analysis. (C) 2004 Wiley Periodicals, Inc.