Intermittent preventative treatment (IPT) is a new approach to the prevention of malaria in this situation. IPT involves the administration of an anti-malarial to children at risk for malaria at fixed times, even if they are not infected. To investigate how effective this approach might be in Senegal, a trial has been undertaken in which 1136 children aged 6 weeks to 59 months were given a single dose of sulfadoxine pyrimethamine and artesunate on three occasions during a three-month rainy season and the incidence of clinical malaria in these children was compared with that in a group of children who received placebo. Additional observations were made on the incidence of side effects in children in the two groups and on the impact of IPT in children (IPTc) on markers of drug resistance in children whose blood films were positive for Plasmodium falciparum.