In this study a capillary electrophoretic method is described for the identification and quantitation of the main degradation product napthylacetyletylenediamine (NAED) in naphazoline HCl bulk drug. The effect of temperature, operating voltage, and electrolyte concentration on the resolution was determined by using a multivariate experimental design. The separation was achieved at 15 kV, on a 70 cm (62 cm effective) x 75 mu m I.D. capillary at 20 degrees C using 0.1 M, pH 3 phosphate buffer as background electrolyte. The method was validated and satisfactory specificity, linearity, precision, and accuracy results were obtained.