A capillary zone electrophoretic (CZE) method was optimized for the separation of five angiotensin II receptor antagonists (Losartan, Irbesartan, Valsartan, Telmisartan and Eprosartan) and two of their metabolites (EXP 3174 and Candesartan M1) by means of experimental design methodologies. The aim of this study was to define rapidly experimental conditions under which the analytes can be resolved for quantitation. The effects of the buffer (pH, concentration and composition), the organic modifier and voltage were studied. Critical factors were Identified in a screening design (fractional factorial design) and sequentially an optimization design (central composite design) was used to choose optimal conditions for separation. The most favorable electrophoretic conditions were found by setting the resolution at a threshold value (Rs greater than or equal to 1.5) and minimizing, if possible, analysis time. Successful results were obtained with a 50 mm potassium dihydrogen phosphate:boric acid (25:75 v/v) buffer at pH 5.5 in the presence of 5% methanol and application of a 25 kV voltage. Analysis time was 8 min in a conventional fused-silica capillary (50 cm effective length) in a normal cationic mode (anode at the inlet and cathode at the outlet) after hydrostatical sample injection for 30 s.