Passive case detection was used to recruit children aged 6-59 months with uncomplicated malaria using a slightly modified version of the standard WHO in vivo method for assessing therapeutic efficacy of anti-malarial drugs .Children seeking care at the selected health centres were screened for eligibility to join the study, enrolled and followed up for 14 days. If a child's axillary temperature was >=37.5 ºC and no obvious cause of fever other than malaria was found on clinical examination, about 500 ml of blood was drawn into a micro-container containing EDTA. Microscopic diagnosis of malaria and measurement of packed-cell volume (PCV) were performed immediately after samples were received in the laboratory. After enrolment, further clinical examinations were performed on days 1, 2, 3, 7, and 14. In addition, the caretakers were advised to bring children back to the health centre at any time between day 1 and day 14 if the child's condition did not improve. Thick and thin blood films and filter paper blood spots were prepared on days 0, 3, 7, 14 and at unscheduled visits.