The alkaloidal components of the Bhutanese medicinal plant Corydalis calliantha Long, which is used for the treatment of malaria, have been assessed. Four known alkaloids, protopine (1), scoulerine (2), cheilanthifoline (3) and stylopine (4) are reported from this plant for the first time. The protopine alkaloid, protopine, and the tetrahydroprotoberine alkaloid, cheilanthifoline, showed promising in vitro antiplasmodial activities against Plasmodium falciparum, both wild type (TM4) and multidrug resistant (K1) strains with IC₅₀ values in the range of 2.78–4.29 µm. Such activity had not been demonstrated previously for cheilanthifoline. The results thus support, at a molecular level, the clinical use of this plant in the Bhutanese traditional medicine and identified cheilanthifoline as a potential new antimalarial drug lead. Copyright © 2009 John Wiley & Sons, Ltd.