Hyperparasitaemia as an indicator of severity or poor prognosis in falciparum malaria and response to oral antimalarial therapy were evaluated in an outpatient study of 77 consecutive African children from an endemic area. At presentation, clinical illness was graded as mild in 37, moderate in 14 and severe in 26. There was no evidence of renal, hepatic or cerebral complications. Clinical response to oral antimalarial drugs was characterized by rapid and uneventful recovery from illness in all but one patient who required hospital admission with prompt clearance of parasitaemia and fever within 96 hours. It is concluded that greater than 5% parasitaemia may be well tolerated by semi-immune African children. Semi-immune subjects with hyperparasitaemia and no other evidence of severe or complicated disease in an endemic area may well be treated with oral antimalarials providing the infecting strain is fully sensitive to the drug chosen and the drug is rapidly absorbed.