Main conclusion An ABCB-type transporter for sanguinarine, a benzophenanthridine alkaloid, was isolated from Argemone mexicana seeds. An ABCB-type transporter, AmABCB1, was identified in a transcriptome from unfolding seedlings of A. mexicana by its amino acid sequence identity to previously characterized alkaloid transporters from Coptis japonica and Thalictrum minus. Expression analysis revealed mature seeds as its main location; meanwhile, in vitro assays in yeast cells showed that AmABCB1 had uptake and efflux activities for sanguinarine and berberine, respectively.