A sensitive, simple, rapid and reliable HPLC-DAD method for the analysis of the benzylisoquinoline alkaloids (BIA's) content in Argemone mexicana (Papaveraceae) is presented. This method allows the simultaneous separation and quantitation of berberine (Bn), chelerythrine (C) and sanguinarine (S) in extracts from A. mexicana tissues, reducing time of analysis in comparison to previous reports. Alkaloids were separated on a C18 Hypersil Gold column using an acetonitrile gradient (20 to 70%) in 1% acetic acid in water. Alkaloids were identified based on retention times and UV spectra and quantified at 254 nm. Linearity between 0.5-20 µg mL -1 was observed for Bn, C and S, with limits of detection (LOD) and quantitation (LOQ) of 0.11 and 0.33 for Bn, 0.10 and 0.30 for C and 0.05 and 0.15 for S, respectively. Maximal intra-and inter-day variation values were < 0.49% in all cases, with alkaloids' recoveries higher than 95%. System suitability tests (SST), including resolution (Rs), retention factor (K'), selectivity (a), tailing factor and number of theoretical plates were performed according to the United States Pharmacopeia (USP), fulfilling recommended values. The method proved to be efficient and reproducible when analyzing different tissues of field-collected A. mexicana plants.