Little is known about changes in laboratory values of children with imported falciparum malaria. Of 192 children, 69% had parasitemia of 2% or less and 64% had platelets <150 x 10/L. In 20%, parasite counts rose within 12-24 hours of starting treatment before falling, whereas the platelet counts dropped in 45% but returned to normal levels within 5 days. Hemoglobin values were <10 g/dL in 31% at presentation and dropped in 61% at 5-21 days after treatment, but did not fall below 6.8 g/dL in any case. Blood cultures were negative in all children. Hyponatremia (n = 16), jaundice (n = 4) and hypoglycemia (n = 0) were uncommon. Thus most children presented with abnormal laboratory values, which initially worsened in a significant proportion, but none required active intervention once therapy was initiated.