In view of the challenges to identifying an effective malaria treatment for infants in Indonesia, the proposed study has been designed to evaluate the effectiveness of delivering early detection and prompt treatment with DHP at 2, 3, 4 and 9 months of age, linked to local immunization programmes delivered at village health posts (Posyandu), in an area with high drug resistance levels to both P. falciparum and P. vivax. The effectiveness of this approach will be compared to the current practice of passive case detection. We will also define the efficacy and pharmacokinetic profile of DHP in infancy and monitor the safety and toxicity of its use.