Asymptomatic schoolchildren in Guinea Bissau were given approximately 10 mg of quinine/kg body weight once daily during 5 days (n = 15) or 3 days (n = 16) for treatment of P. falciparum. Five children had parasitemia on the seventh day of follow up. Adverse reactions were reported by 12 children during treatment, mainly mild tinnitus, dizziness and vomiting. Single daily doses were less effective than the divided doses previously used by us for the same short time period and also associated with more frequent adverse events.