This study will evaluate the efficacy of the treatment recommended by the National Malaria Programme in Guinea-Bissau as compared to a higher dose of chloroquine and to another anti-malarial drug, amodiaquine. The genetic basis of the parasites for developing resistance will be examined. Children coming to Bandim Health Centre with symptoms of malaria and a positive malaria test will be included. The children will be visited and malaria films will be obtained weekly until day 35. In case of a reappearance of parasites the children will be re-treated with sulfadoxine/pyrimethamine.