The effect of the intermicellar exchange on the size control of nanoparticles synthetized in microemulsions has been studied by computer simulation. The employed algorithm includes a reactant exchange parameter, k, which can be related to the dimer life time. This parameter, k, has a big influence on the final particle size, except in the case that one of the reactants is in a big excess. The combination of this reactant exchange parameter and the surfactant film flexibility allow us to discuss the material interchange mechanism via encounter pair or via fused dimer.