A high-performance liquid chromatographic (HPLC) method with electrochemical detection (ED) using a monolithic column was developed and validated for the simultaneous quantitative determination of aniline, 2-aminobiphenyl, and 4-aminobiphenyl in diphenylamine samples. The proposed HPLC method provides a shorter analysis time as compared to previously reported ones (less than 4 min). Method validation was performed in terms of sensitivity, repeatability, linearity, accuracy, detection limit, and quantification limit. It is found that the method has high accuracy and precision. The limits of detection obtained were 0.23 ng/mL for aniline and 0.30 ng/mL for 2-aminobiphenyl, 4-aminobiphenyl, and diphenylamine. © Pleiades Publishing, Inc., 2006.