Most countries in the Americas have adopted the WHO Global Strategy for Malaria Control, which relies on prompt and effective antimalarial treatment as the major means of reducing malaria morbidity and mortality (WHO 2008). The ultimate success of this strategy rests on the ability of ministries of health to provide antimalarial drugs with proven efficacy. Although a wide variety of methods have been used to assess resistance to antimalarial drugs in vivo methods, in vitro drug sensitivity testing, and molecular analyses, most national malaria control programs rely on data from in vivo efficacy trials to assess the efficacy of the current first- and second-line drugs and to decide if charges in malaria treatment policy are needed.