1.1 Mass drug administration as a public health tool In the 1950s, the WHO included mass drug administration (MDA) with antimalarial drugs as a tool for malaria control in 'exceptional conditions when conventional control strategies have failed'. Subsequently, MDA has received little attention until the introduction of artemisinin based combination therapy (ACT). The principle aim of MDA is to interrupt malaria transmission by clearing the population of sexual stage parasites, gametocytes, prior to the transmission season (figure 1). Gametocytes are essential for propagation of the disease and elimination of gametocytes will result in a reduction in malaria transmission. As a consequence, a successful MDA will reduce the burden of disease in a population and is expected to have little influence on the development of protective immunity in areas of low transmission intensity. In Africa, only one large scale MDA study was conducted in the last 10 years. That study, conducted in The Gambia using sulphadoxine-pyrimethamine (SP) plus a single dose of artesunate (AS), failed to show a significant impact of MDA on malaria transmission.1 Possible reasons for this failure are the limited impact of the drug regimen (a single dose of AS) on malaria transmission, the incomplete coverage, the relatively high transmission intensity in the area and the migration of individuals between villages. Here, we propose to conduct an MDA study in an area of very low malaria transmission intensity in Tanzania.