Five extracts from the tropical plant species Triphyophyllum peltatum, Ancistrocladus abbreviatus and A. barteri, and six pure naphthylisoquinoline alkaloids derived from these species have been examined for their antiplasmodial activity. These species are well-known in the traditional medicine of West Africa and are used for the treatment of fevers, malaria and other diseases. The extracts and alkaloids were tested against the asexual erythrocytic stages of two strains of Plasmodium falciparum in vitro (K1/chloroquine-resistant and NF 54/64, clone A1A9/ chloroquine-sensitive). Incorporation of 3H-hypoxanthine was measured in the presence of the test substances after 42 hr of incubation at 37°. All extracts and three alkaloids displayed activity. The two most potent compounds were dioncopeltine A and dioncophylline B. Structure-activity considerations indicate two possible criteria for antiplasmodial activity: an R-configuration at C-3 associated with the absence of an oxygen substituent at C-6 and the absence of N-methylation. © 1994.