We propose a longitudinal cohort study to evaluate the identifiable causes of treatable fever among 1000 malaria-negative children presenting to outpatient health clinics in Miono, Bagamoyo District, Tanzania using a variety of clinical, microbiological and serologic methods. In addition we intend to follow these 1000 malaria-negative children for up to 91 days or until their next malaria infection to assess their clinical progress and need for further malaria treatment. To compare the relative benefit of providing antimalarial treatment even to malaria-negative children, half of the participants will be randomized to receive first-line treatment for malaria as currently recommended; the other half will receive treatment only for other identified illnesses.