The polymerization of butyl methacrylate in three-component microemulsions prepared with the cationic surfactant dodecyltrimethylammonium bromide is reported here as a function of monomer and surfactant content in parent microemulsions, type and concentration of initiator, and temperature. Fast reaction rates and high conversions are achieved in all cases. Final latexes are bluish-opaque and stable, and contain spherical particles with diameters in the range of 20 to 30 nm, depending on composition of the parent microemulsions and reaction conditions. Each of these particles is composed of a few macromolecules of high molecular weight (2 to 4 X 10(6) Dalton). Both particle size and average molecular weight remain constant throughout the reaction, suggesting a continuous nucleation mechanism. Analysis of the molecular weight distribution indicates that the controlling termination mechanism is chain-transfer to monomer.