Hydrodynamic and electrostatic effects in microfiltration of electrolytes, with 0.2 mum polycarbonate membrane, were evaluated using a 2(4) variables factorial design, expanded to a central composite design. The process variables studied were pH, applied pressure, NaCl concentration and stirring rate, response surface curves being established. An interaction between stirring rate and NaCl molarity was observed. The design results suggested salt rejection by the microfiltration membrane and the experimental data confirmed osmotic pressure effects. These experimental findings should be taken into account in the design of microfiltration processes of colloidal particles process fluids, as unsuspected salt deposits on the membrane surface can be detrimental to membrane selectivity. Higher fluxes were obtained for acidic electrolytes (pH 5), medium transmembrane pressures (12-16 psi) and electrolyte concentrations up to 1 M. This paper also illustrates how to implement a simple methodology for optimization of microfiltration applications with membranes with different chemistries.