Parasitol Res (2008) 102:1227–1234 (Nzila et al. 2005a) and that its activity is not increased by the addition of PBN, a well-known potentiator of antifolate activity (Hooijberg et al. 1999; Nzila et al. 2003). All these observations support further that some features of antifolate anticancers in P. falciparum are different from those found in mammalian cells. To further study the mechanism of action of MTX, we explored the in vitro interaction of MTX with 16 existing antimalarials. We did not find any synergistic combination; MTX has an additive effect with all tested antimalarials, except with PNR and PQ. Thus, MTX could be developed with any of the tested drugs as combination therapy, except with PNR and PQ. We have demonstrated that P. falciparum has unique features as regards folate metabolism, and some of these features could be exploited to develop antifolate anti- cancers to treat malaria. For instance, TMX could be combined with 5-Me-THF as an antimalarial, and the use of MTX in the treatment of rheumatoid arthritis indicates that this drug has the potential to become an antimalarial. Plans to test MTX in vivo for the treatment of malaria are under way. Acknowledgments We thank the director of the Kenya Medical Research Institute for permission to publish these data. Part of this work was supported by Pfizer-Royal Society Award, UK (to AN) and the EU Commission under Framework 6 as part of the AntiMal Integrated Project 018834. AN is a European & Developing Countries Clinical Trials Partnership (EDCPT) senior fellow and LM is an EDCPT Ph.D.-funded student. The experiments comply with the current laws of Kenya. Open Access This article is distributed under the terms of the Creative Commons Attribution NonCommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. 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