Study subjects received their monthly chemoprophylaxis at their local health centre under direct supervision by staff of the health centre identified by the health centre and trained to take this important role in the study. Health centre staff were provided with a list containing the study number, photographs and randomisation group of each study subject. Study subjects were observed for 30 minutes after dosing and if vomiting occurs within 30 minutes, the dose was repeated. S/P (tablets containing 500 mg sulfadoxine/ 25 mg pyrimethamine) will be given at an approximate dose of 1.25 mg pyrimethamine/25 mg sulphadoxine per kg. Enrolment of patients started in July and surveillance continued until end of malaria transmission season.