All households in the Dodowa sub-district with at least one child 6 months to 5 years who do not register in the pre-payment scheme for the year will be eligible to participate in the study. The information will be obtained from the data base of households at the DHIMT offices. This sub-district, which is mainly forest with an estimated 2003 midyear population of 30,154, has been selected because earlier studies have shown that it has the highest incidence of malaria in the district. Household heads or their representatives will be invited to either of three locality meetings based on distance from the health facility, where the study will be explained to them and consent sought for their participation in the study. Those agreeing to participate will have their particulars recorded and enrolled into the study. They will then be randomized into two groups using the procedure already described. Baseline data collection including haematological, anthropometric assessments and interviews will then be carried out on all participants and slides for parasites in a random subset. Background variables about the household including known risk factors for malaria such as type of housing, use of insecticide treated materials, use of other preventive measures and some indicators of household wealth will be documented. Children found to have haemoglobin count less than 6g/dl, fever or a history of fever and patent parasitaemia will be treated according to local guidelines; this will not be a reason for withdrawal from the study.