A polymerization method, currently proposed by the authors (Go et al., 2002), for producing micron-sized polymer particles was examined. Soapfree emulsion polymerizations of styrene with an amphoteric initiator, 2,2'-azobis[N-(2-carboxyethyl)-2-2-methylpropionamidine] hydrate, were carried out in a range of initiator concentrations (4-10 mol/m(3) H2O) at a fixed pH of 8.3 adjusted with a buffer system of [NH3]/[NH4Cl]. Highly monodisperse polymer particles could be obtained with this method. The coefficients of the variation on particle. size distribution were less than 2%, and the average particle sizes were in a range of 2.5-3 mum. To produce larger particles, applicability of a simple method to the present polymerization was also examined. The method employed was monomer addition during polymerization. This method enabled the production of polymer particles with an average size of 3.8 mum and a coefficient of the variation of 1.3%.