3.1 Study area The proposed study area is an area in Lower Moshi that has been part of ongoing activities of the Kilimanjaro Christian Medical Centre/Joint Malaria Programme in since 2002 The study area is characterised by a very low transmission intensity with an entomologic inoculation rate (EIR) of 3.4 (95% CI 0.7 - 9.9) infectious bites per person per year. Despite low transmission intensity, an estimated 300-400 clinical malaria cases occur yearly, predominantly in the transmission season. In the area, 4 isolated villages were selected, mapped and censused. Malaria transmission in the villages was characterised by weekly mosquito catches and two cross-sectional surveys for parasitological parameters. Villages are comparable in entomologic and parasitological characteristics and parasite carriage as determined by microscopy (1-3%) and molecular detection techniques (30-40%) is equally distributed over different age groups (NIMR/HQ/Vol.IX/343). Two health facilities exist in the study area, both serving three villages. The health facilities are participating in passive case detection since February 2006. For the proposed study, clusters have been defined using a completed map of the study area where the coordinates of each individual house was mapped using geographical positioning system (GPS). The minimum distance between clusters is 1 kilometer. MDA with the gametocytocidal drug combination will be undertaken in approximately 8 clusters, MDA with a placebo in the other clusters. Migration in the study area will be carefully monitored by community workers. Balozi's will be actively involved in this part of the study. During a cross-sectional study that was carried out in the preparation phase of this study >98% of the individuals indicated that they were permanent residents of the area and to sleep in their house every night of the year. Possible migration of individuals during the follow-up period will be included in determining the minimum coverage of the MDA.