Data generated by this study will provide a snapshot of the current situation regarding P. falciparum sensitivity to ACTs in Western Kenya. By having subjects in one of the study arms receive artesunate and then the partner drug after completion of the artemisinin phase will enable the accurate evaluation of the artemisinin derivative without the confounding influence of the partner drug. Sequential administration of the components of an ACT drug is recognized by the WHO as one of the ways in which ACTs can be administered. There will be close follow-up of the subjects throughout the duration of the study, and as such, subjects who fail to respond adequately will receive prompt rescue treatment. Since it is largely expected that most subjects in Western Kenya will have satisfactory responses to ACTs, data from this study will provide baseline information regarding parasite characteristics when compared to data from Thailand, an area that has reported resistance to ACTs. This, in turn, will potentially enable the identification of key markers, both in the host and the parasite, that may assist in the early detection of resistance, and also to better understand the development of resistance to ACTs. As such, the data generated from this study, both on its own and when compared to and pooled with data from similar studies that will be conducted in Peru and Thailand, will potentially inform both local and international policy regarding ACT use for the treatment of uncomplicated P. falciparum malaria.