Recent, randomized controlled trials conducted in areas of perennial malaria transmission have shown that intermittent preventive treatment (IPT) given at the time of vaccination reduced the incidence of the first episode of malaria and severe anaemia during the first year of life by more than 50% without there being any rebound in the subsequent year. However, in countries such as Mali, where malaria is highly seasonal and prevalent in older children, IPT in infants may not be the optimum way in which to use antimalarial drugs to prevent malaria. An alternative approach is to give intermittent preventive treatment to children at risk just during the rainy season. Here we propose (i) to evaluate the impact of two seasonal IPT (sIPT) with Sulfadoxine-pyrimethamine (SP) given at 8 weeks interval on the incidence of malaria disease in children of 6 months to 10 years in an area of seasonal transmission, in Kambila, Mali; (ii) to assess the impact of this strategy on the in vivo response of P. falciparum to SP; (iii) to assess the potential rebound effect of this strategy on the subsequent transmission season after the cessation. Children 6 months-10 years in Kambila, Mali will randomized to receive either IPT with SP twice at 8 weeks interval or no IPT during the transmission season and will followed up for 12 months. Subjects will be also followed during the subsequent transmission season to assess possible rebound effect. Clinical malaria cases will be treated with SP and followed for 28 days to assess the in vivo response during both periods.