Could widespread use of insecticide-treated bednets (ITNs) have a major and sustainable impact on the Africa rural malaria problem? Is there a negative impact on older children who have not build up resistance to the disease because of protection when they were younger? Would providing ITNs free of charge cost-effective? The London School of Hygiene and Tropical Medicine, together with the Tanzanian National Institute of Medical Research, studied how effective nets, treated with insecticide, were against malaria in children in Tanzanian villages, 3-4 years after the nets were introduced.