In December, at the end of the malaria transmission season, a cross-sectional survey of all the children enrolled in the study was undertaken in all the villages. Information was obtained on demographics, bed net usage, a clinical history was obtained and a physical examination performed, including abdominal palpation for splenomegaly and measurement of height, weight and axillary body temperature. A finger-prick blood sample was obtained from all the children taking part in the cross-sectional survey for preparation of blood films, a filter paper sample and determination of the haemoglobin level.