Antimalarial activity of anthothecol, a limonoid of Khaya anthotheca (Meliaceae) against Plasmodium falciparum was tested using a [(3)H]-hypoxanthine and 48h culture assay in vitro. Anthotechol showed potent antimalarial activity against malaria parasites with IC(50) values of 1.4 and 0.17microM using two different assays. Also, gedunin had antimalarial activity with IC(50) values of 3.1 and 0.14microM. However, the citrus limonoids, limonin and obacunone did not show any antimalarial activity. The antimalarial activities were compared with the three currently used antimalarial medicines quinine, chloroquinine and artemisinin.