Microbeads consisting of a stainless steel nucleus covered with a layer of poly(styrene-co-divinylbenzene) have been synthesized. To determine the influence of several operation variables in the characteristics of the final product, a 2(IV)(8-3) fractional factorial design of experiments was conducted. Eight factors were studied in 32 experiments instead of the 256 experiments required by a full design. The process responses were the thickness of polymeric layer, the absence of particle agglomeration, and the total amount of polymeric material in the nonagglomerated particles (global yield). Empirical equations relating the values of each response to the coded values of the levels of the significant factors were obtained. The results showed that the thickness of polymeric layer response was influenced in a positive way by prepolymerization and double polymerization but in a negative manner by the addition of ammonium hydroxide to the reaction mixture. By contrast, in the absence of particle agglomeration response the factors with significant influence were the same as before, but the effects were the opposite; i.e., the addition of ammonium hydroxide had a positive influence but prepolymerization and double polymerization had a negative effect. Thus a new response-global yield-was designed in order to achieve a compromise in the operating conditions. It was observed that the best conditions to obtain the maximum value of this response involved operation with double polymerization, without ammonium hydroxide, and without prepolymerization.