Less than a year after Artemisinin-based combination therapies (ACTs) were recommended for the treatment of falciparum malaria, concerns about artemisinin resistance development along the Cambodian-Thai border were voiced. Artemisinin resistance has been poorly characterized, and is difficult to detect by classical laboratory approaches.  In-vitro tests have not consistently detected reduced pharmacodynamic responses to artemisinin drugs, and molecular markers conferring artemisinin resistance have not yet been determined.  This study aims to assess the degree of artemisinin resistance in adult and pediatric subjects presenting with uncomplicated falciparum malaria in Western Kenya. The study treatments will be Artemether Lumefantrine (AL) and Artesunate Mefloquine (ASMQ). In order to accurately evaluate the artemisinin derivative without the confounding influence of the partner drug, ASMQ will be sequentially administered. In-vivo and in-vitro methodologies, including pharmacokinetic methods, will be employed. 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 Ghana, Peru and Thailand, will potentially enable the identification of key markers that may assist in the early detection of resistance, and also to better understand the development of resistance to ACTs, and thus inform both local and international policy regarding ACT use.