The study will entail two consecutive years of prospective 28 day in vivo drug efficacy studies carried out during the rainy season in three different malaria transmission sites: Koro (rural town with 71% of resistance to MQ at a lower dose of 15 mg/kg), Pongono (rural town with little exposure to antimalarials) and Faladje (rural village with > 30% of chloroquine resistance). Children aged 6-59 months with clinical symptoms consistent with malaria will be enrolled in the study after screening for fever (axillary temperature >=37.5 C) and malaria asexual parasites identified by microscopic examination of thick blood films.