This is part of a multicentre trial looking into antimalarial resistance within a series of Intermittent Preventive Treatment of malaria in Infants (IPTi) studies. IPTi is a promising intervention to reduce malaria in infants in malaria endemic countries. 3 doses of antimalarial drugs are given in the first year of life to asymptomatic infants at the time of 2nd and 3rd Diptheria, Tetanus and Pertusus immunisation and again at 9 months of age at time of measles immunisation. In the current Kilimanjaro IPTi study we are comparing 3 antimalarials (Mefloquine MQ, sulfadoxine/pyremethamine SP and chlorproguanil/dapsone CD) against placebo for IPTi in 2 transmission zones. Two published studies using SP for IPTi have shown different efficacies for this intervention. The first study (Schellenberg et al 2001) showed a 62% reduction in clinical cases of malaria and the second (Chandramohan et al, 2005) showed only a 25% reduction in clinical cases of malaria. The two sites differ in several ways, the first was carried out in an area of moderate to low transmission with a moderate rate of SP resistance in Tanzania and the latter was carried out in an area of intense but seasonal malaria with a low rate of SP resistance in Ghana. The current IPTi study is being carried out in a site of high transmission with expected high rates of SP resistance. Data from a site 100km away indicates SP efficacy to be 55% (Mutabingwa et al, 2001). There is no data on SP or other study drugs at the ongoing study sites.